I was worried about heat building up as well. If you look at how I did things, the double sided tape attaches the modules to the aluminum reflector in the light fixtures. It's pretty hard for the tape to get hot when attached to such a good heat conductor.
My trailer has mixture of 19 single and double bulb fixtures. None of the modules have come detached/loose in any of the fixtures in spite of taking the trailer over some very rough roads, including logging roads.
I also used genuine 3M double sided tape. I got it at Home Depot.
