Hey guys i was wondering what was better to place the tank behind the Seat or in the area under the steering wheel (like Racing Go-Karts)??

due to firewall rules i'd say behind the seat.

due to closeout rules you have to have a floor so there is no reason why you can't put the tank under that as your firewall, under the seat has the added safty advantage of not being wedged near the exhaust and less weight transfer as it empty's, although that is a relativly small amount. We've always ran it under our legs, the biggest problem has always been the filler neck location

see what i was thinking for the tank is use a clear plastic tube for the filler neck and run it along the frame near your elbow or something to the conventional filler neck location behind the drivers shoulder between the engine and fire wall

yep, that's pretty much what we've ended up doing

Would their be any dynamic effect on the car having the fuel weight relatively to the front?

I don't want to go under the seat because of the raise in the CG.