I put a 3/32" or 1/8" balsa platform in the fuselage. Then wrap the battery and receiver in foam. Then wrap the foam with a couple (2) layers of masking tape. Get some INDUSTRIAL STRENGHT self adhesive velcro. Adhere one piece to the battery/receiver. Have the other piece LOOSELY attached to the 1st piece. Move them around until you find the correct spot.

Once you have found the spot, remove the covering from the adhesive on the loosely attached piece. GENTLY press in place.

For this step you may need to use the tip of a #11 blade to hold the loosely attached piece in place. Remove the battery/receiver and firmly press the second piece of velcro in place.

THIS IS THE KEY STEP. The adhesive on the velcro is going to loosen its grip on the balsa in a couple of months (I have had no problems with the masking tape after 1 1/2 years). To prevent this take some thin CA and go around the edge of the velcro attached to the balsa. Let dry for a few hours and put your battery/receiver in place, pressing firmly. If you need to remove either one, pull up firmly and it will come loose (the velcro really adheres to each other quite well). This installation will hold even if you "lawn dart" the plane. Don't ask how I found out about that part.