Gap between roof and front cap

When I first bought my motorhome (12 years ago) I noticed a lot of caulking on the left side of the seal between the one piece fiberglass roof and the front cap. It was obviously that there was a gap there they needed to fill. Over the years I've had a leak problem at the seal and I've added more caulking to it. My motorhome has spent most of it's life indoors so I only see the leak when I'm using it and it rains or when I've washed it, so hopefully not too much damage has been done.

I decided to get up there yesterday and remove all the old caulking and then redo the seam with Eternabond tape. Once I got a lot of the caulking off, I noticed that the gap is bigger than I would have thought. Basically the roof and the front cap come together and on the left side the roof has a slight dip to it. So the roof at the bottom of the dip, is close to a half inch below the front the cap. I can stick my finger in the gap. There is a painted metal trim piece over the top of the seam that is screwed into the roof. The trim piece sits flush on the front cap, but it is up to almost a half inch (maybe a third of an inch) above the roof. I'm pretty sure this dip in the roof had been there since assembly and they just filled it in with extra caulking because I've seen that since the beginning. So it's not the structure or anything under it giving way.

So the question, I'm wondering how to fix it. Ideally I'd like to get the dip out of the roof, but that is not a do it yourself project and I don't even know if a RV body shop could do that. So I'm contemplating other fix ideas. I'm thinking about removing the trim piece so I can completely see the seam between the two pieces. And then filling in any gaps somehow with the trim piece off, and then putting it back on re-caulk and then put the Eternabond over the top and double or triple it up in that area? It's pretty obvious that when they assembled the motorhome they fitted the fiberglass pieces and then put the trim piece on without any caulking underneath it and then caulked the joints as the last step. So I'm thinking if I get it good and sealed underneath that I can make sure it doesn't leak again.

Anybody got any better ideas?

Class A

msmith1199
Explorer II
Mar 24, 2016
I went down to an RV Body shop that is close by and came across a very nice person there. I showed him the photos and told him I'm trying to fix this myself and asked him if that was possible. He spent about 20 minutes telling me what I need to do to fix it and even took me out in the shop and showed me a trailer they were working on that had a very similar issue. I was very pleased that he would take the time to show me how to fix something myself that they charge people to fix. So I told him I was going to give it a try but if I couldn't fix it correctly I'd bring to him just because he was so helpful.

As to things coming loose, I don't think that's the case. As I said several times the motorhome came with this issue out of the factory. I couldn't see the gap because of the caulking they put in it, but because of the amount of caulking they used, I could tell that the roof and front cap weren't even. It is very possible that the screws were not put in properly or down deep enough, but they didn't come loose.
msmith1199
Explorer II
Mar 24, 2016
Dale, your tips are similar to what the RV body guy said. I'm going to remove that existing trim piece and then hopefully I'll be able to see what's causing the problem. I'll clean everything up and get bigger screws to put it back down. I'll decide on new holes when I see what's under there. And I will use stainless steel screws as I can see the heads of some of the old screws and they are rusted, even though they did have a dab of caulking on top of each one of them.
msmith1199
Explorer II
Mar 24, 2016
Okay, my quick little project to remove the caulk and replace it has turned into quite the little mess. And I'm learning a lot about how crappy RV's are made. It wasn't that the screws had come loose, it was that the screws were never long enough to begin with and they appear to be the wrong type of screw. They are self tapping sheet metal screws and I think about 1" long. I cleaned the sealer off the top of them and used my drill driver to remove them and all but two of the just spun and would not come out. So they weren't even driven down into the underlayment plywood. The little self tapping part at the bottom of the screw also causes you to lose some of the thread. And this was the entire length of the seal, not just the part that was the problem. So the screws were basically just sitting there and not really holding anything down. The sealer was holding the trim piece on. The screws did go through both the roof fiberglass and the front cap so they were at least acting as pins hold those two together.

Dale, I notice you said you used 1" screws. Did you drive them all the way down into the plywood? I installed a new flat screen TV so I can pull it out and see a 3/4" thick sheet of plywood up there. I'm not sure if the roof fiberglass is right on top of that or not. I may have to pull a screw out of my satellite dish because I can see those coming all the way through the plywood that I can see. I'll see how long those are and use the same length to put the trim back on.

I also have a snake camera at home. I'm going to bring that to my shop tomorrow and see if I can get a better look as to what's going on under the fiberglass.
rgatijnet1
Explorer III
Mar 24, 2016
At that point on your roof you probably have an aluminum frame member, that has a thin piece of plywood on top of it. Self drilling screws are the right type to use if they were long enough to get through the fiberglass, the plywood, and in to the aluminum. I doubt seriously if you have all wood in that joint location. Perhaps a 1 1/2" screw would be long enough. You may have to pre-drill the holes in to the aluminum or just use longer self-taping screws.
msmith1199
Explorer II
Mar 24, 2016
Steel frame, not aluminum. Self tapping sheet metal screws are not going through steel.
Bruce_Brown
Moderator
Mar 24, 2016
If it were mine I'd take the entire strip off, clean everything up, then head to Home Depot and get a new, wider piece of aluminum or steel. Install that staggering the new screws in a zig-zag pattern. Start at one end and slowly walk you way to the middle. That should pull the roof and cap together as you work your way towards the center.

When it was all together I'd cover the entire thing in Eternabond.

When I did my TT Rehab I also fixed a bunch of factory mistakes, and not much of the original trim fit the way I thought it should. I used aluminum and it is still working well today.

If you wanted to paint it use a self etching primer first.
msmith1199
Explorer II
Mar 24, 2016
Bruce, I did take the trim off and got most of the old sealant off. Are you thinking instead of reusing the old trim just use a flat piece of aluminum? I can see how that may work. And I do plan on using the Eternabond tape. I bought it about a year ago and have just been putting this project off.

I was actually looking at it and wondering what good the trim piece was even doing at all? Basically it's just acting as a washer for the screws. I was thinking once I figure out what size screw will work, just getting them with a flat head and a washer and leave the trim out. That way I'll have a fairly flat surface to put the Eternabond tape on. If this Etrnabond is everything they say it is, I think that may actually work better anyway. I'll have to give that some thought.
wolfe10
Explorer
Mar 24, 2016
Only concern with Bruce's suggestion is that as already posted, I HOPE you have a structural member under the seam. If so, staggering screws would likely hit on either side of the structure.

If the structure is steel, a magnet will tell you that in 2 seconds. If aluminum, you may have to drill one tiny diameter hole to verify what and where it is.

And absolutely, if the structural member is slightly fore or aft of the seam, use a wider molding, or even make a new one from wider flat stock.
lafrentz
Explorer
Mar 24, 2016
msmith1199 wrote:
Steel frame, not aluminum. Self tapping sheet metal screws are not going through steel.

actually they do very well through steel. just drill a small pilot hole.Based on your pictures, fixing your front cap to roof is pretty straight forward if your a DIY type person,have tools and have some
talent
rgatijnet1
Explorer III
Mar 24, 2016
As mentioned self-tapping screws work very well in light gauge steel framing of about 1/8" or less wall thickness. Any thicker than that and you may have to drill a pilot hole. I would use a hex washer head stainless screw since it will allow you to have more driving force and more area to compress the fiberglass than a Phillips head screw.

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Gap between roof and front cap

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