priming the inside of tubes...and fit
I am little surprised with the fit issues, never saw this so far with two builds. Not sure how the cuts are being made to length, this can roll the edge over etc....nevertheless, it is what it is for your fit, I am not doubting you are seeing real fit issues. I can say what I do for the inside of torque tubes, is to use a spray can of zinc chromate primer, and keep it very thin, really "fogging" the inside more than trying to deliver a paint coating of x mil thick. At the ends I wipe clean with acetone, easily removes primer (spray cans are not an epoxy), when assembling (after drilling & deburring) and ready to rivet I spray again and assemble while still wet, if anything, the paint is now a anti-corrosion adhesive and then rivet per call out. I am big believer of chromate-based primers (non-epoxy) inside tubes because the chromate will "migrate" and protect the entire tube surface for a long long time. I personally do not like chromates for a lot of reasons, but the anti-corrosion power is second to none and used correctly, are quite safe.
Dues paid 2017
RV7 built & sold, 500h of pure joy in the air: sold
RV10 slow build & flying & loving it