one of mine was screwed into styrofoam trim that was being held up primarily with double stick tape. I was shocked that it had lasted so long. Fell off on a bumpy road in Louisiana on a long trip a couple years ago. I stopped at a home depot and jury rigged up a support post for it....sadly it's still there. Meant to, but I never went back and did a nicer job of it.
as far as weight limit.... I'd guess that's highly variable...some are attached to wood, some Styrofoam, some apparently to the ceiling (which if like mine is just a thin decorative film over foam)
__________________
|