Blake442 said:I would avoid things like urethane or silicone due to the difficulty of removing them if he or another owner ever removes it.
If you spray the surface you don't want the silicone to bond to with mold release there won't be an issue removing the cover. When you bolt it down with fresh silicone don't tighten it all the way or the silicone will be squeezed out. Just put a little pressure making sure there is a little bead of silicone squeeze out around the panel and let it cure and then tighten it down.
On aircraft they never made gaskets for access panels so that's how we made gaskets that were bonded to the panel but not to the aircraft making them reusable