ORIGINAL: RC-FIEND
Why would you have reservations about old balsa?
Wood no matter what type or kind warps even if you try your best to preserve it in a seal tight container. My worry is trying to pull off a tight snap roll or a fast loop and then an unseen dry rotted section in the wing snaps in mid flight causing a major crash hopefully no hurting any body.
In my line of work , I see doors go from closing without a problem in the summer , to not being able to close at all in the winter. This is caused by moisture being sucked in and out of the wood. So why would (no pun intended) be different ?
Wood that is properly stored does not warp or rot. Woodworkers do this all the time. The key is to keep it properly stored. If the kit has been opened and the wood put back all jumbled then yes, it's probably going to warp. If the sheets and other stock are still bundled and are flat on the bottom of the box then they will remain straight. I too have several old kits and when I look at them the wood is still in excellent condition.