I usually just use a little clear silicone to keep tanks in place.  Never seem to move except in figure 9s. 
Lee TGD

But don't glue it down until you get it at the right height.

In full fuse ships, I make small light-ply "clips"  to go on each side of the fuse (inside).  At the rear, I permanently install a basswood beam across the tank compartment at a height such that the tank plus some foam and shimms can go under it--wedging in the back of the tank.  At the front, the small clips--a notch cut so that you can compress the foam and put another beam in across the tank.  The foam holds the tank up to the crutch and shims, and the compression keeps the beam seated in the clip.  Once the tank height is set, silicone in the removeable piece, and your done.  If the tank needs to move, then cut away the small silicone locks and push out the fron t beam. 

The tank can be removed without removeing the engine this way as long as the cowl alows it.

Sorry don't have any pictures.

Curt

"The best way to guarantee that a tank will leak is to permanently install it."