control locks
If you don't want to use the seatbelts to lock down the stick, try this: make a two plastic disks about 2 1/2 - 3 inches in diameter, glue on some foam rubber/rubber/something soft, drill a 1/4 inch hole in the center of each disk, run a piece of 1/4 inch threaded rod through the holes and put washers, lock washers, and wing nuts on both ends. Slide this assembly in the gap between the aileron and the wingtip fairing and tighten it down(not so tight as to crack things). Repeat using 3/16 inch (or smaller) for the ailerons.
To be honest, I didn't fab mine up. I bought some furniture leg pads (coasters), the kind you put down beneath the legs of the furniture to protect the carpet... works for me.