Thinking about the airframe / coupler and centering ring structure. From what I see, you are building something crazy strong: CR, coupler, CR; all tied together with glassed stringers and all thread rods, all repeated 10 or so times, correct?
If im on track here, this structure “is” the rocket with the G12 airframe being along for the ride. If so, why not assemble all of the couplers, rings etc. outside the rocket and then ‘slide’ the airframe over and screw the airframe yo the CRs. A dozen grade 8 screws per ring would be plenty strong and would negate having to crawl/reach into the airframe to glass and would also address any possible issues with the epoxy grabbing / sizing the couplers
Just thinking out loud, but “removing” the confined space of the airframe may make a lot of assembly easier