Idid the same 4 a 8 year olds radio.. the LHS by me have nitro fuel line in many sizes from 1/2" down try getting a few pieces on by overlaying also try medical tube..They also make a foam hockey tape that works well also just a few layers thick..Or get a piece of UHMW and put it in oven heat to 325 degrees and mold that to brake side of trigger then trim with Dremel tool (when it turns clear its ready to work Use protective gloves so u dont BURN ur fingers..