Two things that I've done that seem to work...FIRST OFF let me say I'm using a home-made PTT, not one that I bought from anyone so this may not work exactly for you the way it does for me.
#1 - to hold the PTT switch in place, I use a common band-aid. I use a hole puncher to punch a hole through the part with the cotton guaze and then just apply the band-aid over the switch and to my finger with the push button sticking through the hole I made. So far, the band aid has been the best solution for keeping the switch from moving. I've tried electrical tape, first aid tape and even sewed an elastic band to attach the switch to but I've gotten the best results with a normal common every day band aid.
#2 - to seal the back of the switch where there are exposed metal leads, I simply coat the back of the switch with liberal amounts of hot glue from my glue gun. I coat the entire back surface of the switch where the leads are, where the wire connects. Then once the glue cools off completely, I use an X-Acto hobby knife (with a brand new blade) to shape and cut away the excess glue so that the switch will fit in my glove. If you don't do this last step, the big glob of glue will keep you from being able to get your finger inside the finger of the glove.
I've had pretty good results with these and use the PTT on my TK and my Vader...and I sweat bucket loads in both of those costumes.