The last item on the coach for the pre-season list was to replace the original skylight over the shower.
There was nothing wrong with mine and it was still somewhat flexible/pliable even being 20 years old this year. There seems to have been a lot of people with cracked and/or broken sky lights in their coaches this past year based on threads on an RV forum that I visit so I figured I would be proactive so as to not ruin a vacation due to a broken skylight.
Mine was not leaking and was properly sealed from the factory but still, I figured there was a better way to mount the new skylight. I have never been a fan of putting screws through the plastic/lexan skylights and allowing all of those stresses and forces to be in such a narrow field. I thought if I could build a picture frame to go around the perimeter of the skylight and then sandwich the fiberglass roof material, inner clear bubble, outer smoked skylight and then the aluminum frame with butyl caulking between each layer it would be a much more uniform and even application of tension and should last another 20 years. Yes, I probably over-thought this and could have just replaced it in the same manner as the factory but I guess I tend to go a little overkill on things.
Here is the original before commencing the project. Other than being a bit chalked out, the skylight was still somewhat pliable and I probably could have gone another year or two. Monaco did a very good job of ensuring it wouldn't leak.
New smoked skylight and mocking up the aluminum frame to gather measurements.
Once aluminum was cut, I beveled the edges and left about 1/16" land remaining for full penetration.
After the frame work was completed I clamped it to the new skylight in order to transfer the screw hole locations to the aluminum frame. This way I didn't need to weaken the new lexan skylight any more by drilling additional holes.
Test fitting one last time.
Original skylight removed, all old butyl putty and lap sealant removed. Prior to reassembly I wiped the entire perimeter down with mineral spirits.
I applied a healthy bead of butyl caulking down around the perimeter and then installed the clear inner bubble. This is used for insulating purposes and creates a couple inches of dead air between the inner and outer bubbles.
I then applied a little thinner bead of butyl caulking, installed the smoked outer skylight, then another thin bead of butyl caulking and then the aluminum frame work and used #8 by 1-1/4" stainless steel tech screws which bit down good and solid to the original roof and sub-structure.
Finally I applied a dose of Dicor self-leveling lap sealant around the perimeter and the screw heads avoiding to get any on the lexan material.
That pretty much concludes the skylight installation.
On a side note, all skylight manufacturers that I investigated when looking for my specific size had one thing in common. They all had caution or warning labels stating to NOT use Dicor self-leveling lap sealant on these skylights. I also saw quite a bit of mention of that on the RV forums that I frequent. The skylight manufacturers recommend using their butyl caulking or a product called SB-140 which is a butyl caulking that goes down pretty nice but definitely does not flow out like a self leveling lap sealant. I am not a chemist but I think it has something to do with the petroleum base of the Dicor and it attacking the lexan of the skylight.
Maybe that is why my original lasted 20 years is because Monaco used a much more dense skylight caulking to adhere the skylight and I only touched up a couple areas over the 15 years that we have owned the coach. When I touched up the areas I did in fact use Dicor, however, I kept it away from coming in contact with the lexan itself and just used the Dicor self-leveling lap sealant to cover cracks in the butyl caulking/putty.
It seems as though the ones I've seen fail online have one thing in common and that was they applied Dicor self-leveling lap sealant directly over the lexan skylight and along those seams is exactly where the skylight cracked and failed. So obviously there must be something to that and I wasn't going to take a gamble and chance it so I followed the warnings and only used the Dicor over the screw heads and outermost seam making sure to keep it far away from the lexan material.
Hope that information is helpful and thanks for looking.
Mike
