[Ant]

I have had this problem, and its simply the wide area of this type of tank design, the pickup shouldn't be in one corner, unless you are going around in circle. Foam doesn't solve fuel surge but it helps, I have had 15g fuel cells and when they run down around one third full they can have fuel pickup problems.
The best way is to either have fore and aft baffles with a swinging gate setup with the pickup in the middle, all this needs to be a snug fit, or an easy way seeing your tank is made, is to make a pot to fit the tank, simply like a big round tin with three cylinders first one slotted at front bottom, then second slotted at back, and central pickup cylinder slotted front , so fuel in the center cant come out on acceleration and cornering, hits the back of #2 under braking and so on, you probably need to draw it - it works!!!!!

I can email you a drawing if you like!

Ant