This stuff is supposed to be used in Fuel Cells with a removable top, and internal rubber bladder.
To load in a fuel cell, you unscrew the top of the can (the metal container containing the bladder) and remove it. The baldder has a bolt on fill plate that is removed, and the old foam removed and replaced with new blocks, trimming for fuel pickup and level check as appropriate. The fill plate is replace, the top bolted back onto the can, and you're done.
While I guess you could stuff the foam down a gas fill tube, the foam is a service item that needs to be replaced every couple years.
A fuel tank should have baffles welded into the tank to control fuel slosh- baffles have small holes that permit fuel to move between the section of tank, but small enough it can't move too quickly and slosh.
I'm thinking that unless you want to totally clean the tank every couple years, you need to be looking elseweher for your solution
