cell foam will not help. A bottom feed tank needs a sump to trap fuel for the corners. Some builders installed a partition in the tank with a trap door that will allow the fuel to move to the rear during acceleration and trap it there when braking or turning. Others built the sump hanging out the bottom of the tank and have small holes in the floor of the tank that feed the sump. That setup required the floor of the tank to be raised up off the pan of the kart. Using a chaser line from the top is effective as long as the floor of the tank is smooth and has nothing the weighted end can hang up on.
If you have to do any welding on the tank be very careful to clean it well enough to insure there are no remaining hydrocarbons left to explode…. speaking from experience here :(