If the Rx and battery are in between the tank and the servo tray, try using plain old kitchen sink type sponges. Cut one to fit the bottom of the bay, cut the next one with holes to fit the Rx and battery, top it off with another uncut one to cover the middle one with the parts in it. It builds kinda like a salami sandwich but, you have to put your own peppers (Rx and battery) in the salami part. Top it off with a little bit of balsa stick stock seasoned with thick CA to the fuselage sidewalls... Yummmy! Like a homemade version of this http://www.jtecrc.com/pillowPacks.htm but tastier...