Neither, wrap it in foam padding to keep the vibration down that can cause the fuel to foam and generate air bubbles in the fuel line.

http://www2.towerhobbies.com/cgi-bin...&I=LXL430&P=ML

You need the stuff to wrap your receiver too, to protest it. Don't forget to put a wrap of tape around the crystal if it is exposed to keep it from vibrating loose. The foam will hold it if wrapped properly though.

Wrap the tank with enough layers to fill the space and it will not slide around either.

Edit - last resort if you don't have any foam, use a fluffy old sock. Sounds strange I know but it will work as a last resort. Wrap loosely and secure with a large rubber band.

Boy, am I gonna hear about this one I'll bet. Try to get the foam if you can