You could use ZIP, it's a silicone you use to seal things, windows etc. The great thing with ZIP is that its texture is like rubber, it never becomes completly hard like plastic. Also, you can remove it all or in parts, it will stick but you can pull it off like rubber. Since it's not hard it wont thump inside your gun like a rock. It wont break your stock while expending and get into every little hole. If it does get into a hole you just take a pair of tweezers and pull it out
http://www.rona.ca/shop/~sealant-zip...811_paint_shop