Best Product To Glue and Seal a Large Hole on the Roof

permanent = 3M 5200 IIRC. but I think I would just install a standard vent cover and raise the panels some.

bumpy

My first thought is you really need to screw it down but not to the existing roof. I would cut wood spacers to fit the gap between the exterior roof and interior ceiling and side to side. Make them a 1/16 or an 1/8 undersized up and down which will help pull every thing tight later. Screw the aluminum you have to the spaces and trim out a piece of 3/8 or so ply and screw that to the spaces from the bottom. This is where undersizing will pull the two covers tight. Use Proflex Sealant under the aluminum and any exposed hardware on the roof. Seal the edges of the aluminum plate Eternabond. Also paint the aluminum before installing.

To make the interior cover look a bit better you can add edge wood to hide the ply layers. Give it a coat of paint to match the interior ceiling color. You could also fill the space between the upper and lower covers with spray foam or fiberglass which will help with heating and cooling plus deaden sound.

If you mounted the panels about 3" above the opening, you could use a vent to fill the hole.

Richard

Outside? Dicor and eternabond tape around the edges. What are you going to do about the ugly hole inside?

I wouldn't use Dicor under the Aluminum sheet since your roof is fiberglass. I would suggest using Proflex Sealant. It is a urethane based silicone that creates a strong bond along with sealing properties. Dicor is meant to be a sealant and not a bonding agent were as ProFlex covers both bases. The Eternabond tape is a good suggestion. Then use the Dicor to seal the edges to keep it from peeling over the years.....Better overkill when it comes to leaks. You can buy all these products at your local RV Dealership

As teachers pet suggested. Just check the type of Dicor you use. There are different ones for different roof types ( material),
and get self leveling.

Dicor Lap Sealant under the plate.. EternaBond Tape over-lapping the edges with Dicor lap sealant on top of the EternaBond edges. When they mounted our Datastorm aluminum baseplate 9 years ago a bedding of Dicor lap sealant was laid on the edges of the plate which was then flipped over and screws driven around the edges which was covered with Dicor sealant.