I have for years mounted PPM Rx's on velcro only and it works fine function wise primarily on pylon racers and the reason to do so is a fanatical effort to reduce weight. Is there a price to pay? Yes of course and that is virtually no crash protection with most crashes resulting in a destroyed Rx. Thats Racing

Of course on the other hand I can also remember mounting Rx's suspended mid air on rubber bands in a caniverous fuselage to protect glass tubes and delicate relays or reeds.

John