It's easier in a flying wing design .

No, really, the CG of a flying wing is farther forward anyway, so having the tank on the CG is easier, and puts the tank closer to the engine, so you don't have the long tubing runs.

Also, on conventional models, the wings come off, unlike on full scales. So you have to have fittings that don't leak fuel all over inside your airplane. More trouble than it's worth on that one.