Got replacement fenders today, they are fiberglass and the side of the RV is fiberglass. The back side is accessible so I could use nuts and bolts (and washers) to attach, perhaps round head phillips screws or something vaguely attractive, and stainless or zinc coated for weather durability. It feels like using any kind of self tapping or wood screw would not hold in the fiberglass well. Anyone know what the factory used? The old fenders are long gone so I have no idea. There's holes from the old ones, no holes in the new fender so I'll probably mark and drill the new fenders to match the old holes.A composites friend recommended washers with a shoulder that goes in the hole to prevent damage to the fiberglass, a good idea.

Use stainless carriage boltswith locking nuts and I use the garage hanger straps with the holes in them for extra support

newman fulltimer wrote:Use stainless carriage boltswith locking nuts and I use the garage hanger straps with the holes in them for extra supportI think one of those straps is still hanging on the trailer, it was in the center, makes sense.

If you use self tapping screws, just dab a little caulk on the back of them where they protrude through the skin on the trailer. It will keep them from vibrating loose. Basically, caulk where there would be a nut if you used a bolt.

Well, upon further inspection it looks like all but the lowest two are not accessible from behind, and the side material for the TT is actually a thin laminated plywood, part of a skin-foam-skin sandwich that makes up the sides. So I need something to bite into that plywood enough to hold the darned fenders on in the wind...The hole pattern is in a slightly different location on these so I do get to make fresh holes where I want them.

Use a dab of marine tex 5200 and they will be on there when the rest of the camper rots away. Just drill a pilot hole, then dip the screw into the 5200 and drive it in. Its there and not going anywhere. Waterproof too.

hardware for attaching fenders | Good Sam Community

joshuajim
Explorer II
Nov 09, 2015
I'vd had good luck with using rivet nuts to attach things through thin paneling or fiberglass walls.
westend
Explorer
Nov 08, 2015
Masterful! It's looking great!
Harlock
Explorer
Nov 08, 2015
Fenders are on! Ended up using stainless pan head sheet metal screws, and a few pan head machine screws where the bite wasn't good, but most of the time I got a good bite on sheet metal.

pilot drilled everything, body drilled the fiberglass fenders.

Only had to adjust one corner on each fender to fit. Fiberglass is easy to file. Used the original center hole, the other holes were not near the original holes so I made new holes completely, which is actually nice.

Still need to seal everything up but otherwise good to go.
Harlock
Explorer
Nov 07, 2015
I did some more inspecting around the trailer and found that after the ply / fiberglass layer there is some sheet metal behind it in that part, so after some test drilling using the old holes it looks like sheet metal screws will indeed do the trick. I am off to the store now to see if I can find some stainless variety, I don't know that zinc coated would hold up, that's the most watery place with the water splashing up from the wheels.
myredracer
Explorer II
Nov 07, 2015
Maybe stainless steel flange head screws or bolts? Available in many different types. Or ordinary stainless steel screws with s/s finishing washers? May need to go to a fasteners supplier to get this.

Proflex caulk would do a pretty good job of holding it in place along with mechanical fasteners esp. since fenders are fiberglass. I recently had to remove some off one of our fenders and I was amazed at how well it adheres to surfaces (except HDPE plastic like some fenders).
BarneyS
Explorer III
Nov 07, 2015
I would think those hole recesses would be ok because you don't want to tighten down on the holding screws too much. Only need enough to hold the fenders on. Seems to me that ordinary SS sheet metal type screws and maybe a washer behind the head would do it. The use of the GE5200 adhesive caulk around the whole thing when installing sounds like a good idea to me also. It comes in both the large caulking gun tubes and small squeezable tubes that you can get at Home Depot.
Barney
Harlock
Explorer
Nov 07, 2015
Here's some pics of one of the new fiberglass fenders. The hole recesses are not as deep as the edges of the fender so there will be a gap between the fender and the side at the screw locations. That would seem to cause unnecessary stress and perhaps I should stack some washers to bush it or machine spacers out of aluminum (I have a metal lathe at home). Sorry no pics of the TT side yet, can get some tomorrow. Gets dark before I get home from work now!
donut_slayer
Explorer
Nov 07, 2015
Use a dab of marine tex 5200 and they will be on there when the rest of the camper rots away. Just drill a pilot hole, then dip the screw into the 5200 and drive it in. Its there and not going anywhere. Waterproof too.
Harlock
Explorer
Nov 07, 2015
Well, upon further inspection it looks like all but the lowest two are not accessible from behind, and the side material for the TT is actually a thin laminated plywood, part of a skin-foam-skin sandwich that makes up the sides. So I need something to bite into that plywood enough to hold the darned fenders on in the wind...

The hole pattern is in a slightly different location on these so I do get to make fresh holes where I want them.
Campinfan
Explorer III
Nov 05, 2015
If you use self tapping screws, just dab a little caulk on the back of them where they protrude through the skin on the trailer. It will keep them from vibrating loose. Basically, caulk where there would be a nut if you used a bolt.