Bigfoot builds a very nice camper shell, then severely compromises it by how they install the roof penetrations. The skylight in the shower on mine leaked just once (wind? tilted the right direction?), I wanted to fix it permanently. There were two basic design issues: the skylight flange is flat and the roof curved, and they attempted to overlap the flanges of the skylight and plumbing vent cover. This resulted in gaps of more than half an inch, which were expected to stay sealed (at least until the warrantee expired) with a huge pile of butyl caulking tape. It did not last long.

First step was to fix the plumbing vent. I cut a short piece of G10 fiberglass tube, slightly enlarged the hole in the roof to fit, and sanded the gel coat back for a good bond. Then bonded the tube into the hole with a fillet of thickened epoxy. Even with no caulking at all, this creates a 1.5" wall that water will have to climb to get into the roof.

Of course the cheap RV caulking that was used on top of the skylight flange had long since failed. While this is secondary to the butyl, it does no good at all at sealing, and only makes cleaning it off a messy chore.

I removed the skylight and cleaned up the mess. The gelcoat was sanded back in preparation for the fix. Note that they somewhat missed the hole required of the shower.

My fix involved cutting a frame from some 1/2" G10 fiberglass sheet, then cutting and grinding the curve of the roof into the bottom of it, leaving the top flat. Grinding fiberglass is an unpleasant chore, obviously they could have molded this shape into the fiberglass shell with no effort at all at the factory.

Fiberglass sheet like this is very strong, but can be cleaved between layers easily. To limit the grinding, I plowed slots at the appropriate depth every 3" or so, then chiseled out the waste and cleaned it up by grinding. It doesn't need to be perfect as it will be set in a bed of thickened epoxy which will fill in the gaps.

Fixing the skylight on BF10.4 - picture heavy | Good Sam Community

19 Replies

HMS_Beagle
Explorer
Oct 16, 2020
The edge of exposed epoxy was painted with PU paint, as epoxy has poor UV resistance. The skylight was set in 3M 4000UV sealant, and no screws were used at all. The sealant is far stronger than the screws, and does not involve drilling 20 leaks into the roof. The new plumbing vent cover was set the same way. It would have looked better if I'd cleaned all the old sealant off the top of the skylight flange, but a little bit of it was still stuck well, and heck - nobody will see it anyway.
HMS_Beagle
Explorer
Oct 16, 2020
The frame was set in West Six10 epoxy. I've already removed the masking tape protecting the roof from squeeze out. The tape going left (towards the camper centerline) is to prevent the frame from sliding off of the roof in the wet epoxy as it sets
Lwiddis
Explorer II
Oct 16, 2020
Excellent posting. Informative.
HMS_Beagle
Explorer
Oct 16, 2020
Here is a view along the contoured edge, You can see the curve of the roof which the flat skylight flange was asked to accommodate. The curve is approximately 3/8", either the flange and skylight must bend that much or you would have to have that much caulk at the ends.
HMS_Beagle
Explorer
Oct 16, 2020
Fiberglass sheet like this is very strong, but can be cleaved between layers easily. To limit the grinding, I plowed slots at the appropriate depth every 3" or so, then chiseled out the waste and cleaned it up by grinding. It doesn't need to be perfect as it will be set in a bed of thickened epoxy which will fill in the gaps.
HMS_Beagle
Explorer
Oct 16, 2020
My fix involved cutting a frame from some 1/2" G10 fiberglass sheet, then cutting and grinding the curve of the roof into the bottom of it, leaving the top flat. Grinding fiberglass is an unpleasant chore, obviously they could have molded this shape into the fiberglass shell with no effort at all at the factory.
HMS_Beagle
Explorer
Oct 16, 2020
I removed the skylight and cleaned up the mess. The gelcoat was sanded back in preparation for the fix. Note that they somewhat missed the hole required of the shower.
HMS_Beagle
Explorer
Oct 16, 2020
Of course the cheap RV caulking that was used on top of the skylight flange had long since failed. While this is secondary to the butyl, it does no good at all at sealing, and only makes cleaning it off a messy chore.
HMS_Beagle
Explorer
Oct 16, 2020
First step was to fix the plumbing vent. I cut a short piece of G10 fiberglass tube, slightly enlarged the hole in the roof to fit, and sanded the gel coat back for a good bond. Then bonded the tube into the hole with a fillet of thickened epoxy. Even with no caulking at all, this creates a 1.5" wall that water will have to climb to get into the roof.

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Fixing the skylight on BF10.4 - picture heavy

19 Replies

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