Do it right or else theres no other way.
OR OR OR OR!
all I can say is...if your willing to do this slightly suicidal attemp.
Resin the outside with 2-3 layers, let them dry, do one side first, then the other side. 3 layers done do the next step
drill a small hole in the back or the front of the gun, pour a cap full of resi nwith hardener into it, swish it around making sure the resin gets everywhere inside. let it sit drying for a month, resin without contact to much air or sun wont dry too fast, you could have a high powered lamp sitting over it too, to keep it hot and have some light shine in, that would make it dry in 1-2 days.