BTW... I used HS-81 servos in mine.

If you wrap the RX in foam, you usually just wedge it into the fuse somewhere, or glue some wood sticks in to hold it in place. I use balsa sticks or popsicle sticks, I just glue them to hold the foam wrapped RX bundle in place. If you use velcro or foam tape, you just stick it to a flat surface inside the fuse. Wrapping in foam isolates it from vibration and protects it in a crash. The foam or velcro tape just helps isolate it from vibration, doesn't help in crash.