I did my helmet in hot glue, however, I also 'filled out' all the pieces that attach by trimming ABD to fit inside and leave a tiny little gap for glue beween the helmet surface and the added ABS. Filled the piece with hot glue, put in my ABS 'shim' and let the glue cool. Then filled the other gap and placed it on the helmet.
I've not had a problem with anything falling off or coming loose, but I've got a lot of glue inside.
I also used hot glue and ABS to place all my electronics in the helmet, but that's because I'm ripping them out soon and replacing my current Radio Shack sound board with a Hyerdyne. When I put that in, I'm going to use a much stronger adhesive.