RE: Rubber bands or Nylon bolts for wing?
The biggest problem I have seen with installing wing bolts in a trainer designed for rubber bands is interference with the aileron torque rod linkage. In four instances I have seen hardwood blocks installed which provided plenty of support for the bolts - and then the blocks were ground very thin, close to the threads, in order to clear the aileron linkages. I have seen three such conversions fail in the air.
I recommend you stick with the rubber bands. If, instead, you feel you must convert to bolts, I suggest you look into the DuBro wing bolt kit. It mounts a plastic threaded block to the outside of the fuselage, leaving plenty of room for reinforcement inside the fuselage next to the aileron linkages.
Good luck,
Dave Olson