Is the car a strip only car? or do you do the street strip thing?
Crazy as it sounds it's be alot easier and cheaper to just install a small 2 or 3 gallon cell under the hood with it's own separate fuel system. That way whatever's in the main tank will be the same all day and you can just top off between rounds.
I personally keep a full tank as long as possible really helps keep my 60's consistent-might be a tad slower than if running on fumes but this is bracket racing!!

, depending on how many rounds I'll watch the gas gauge and if it moves a wee bit I'll throw more gas back in to try and keep the weight the same. But with both vehicles I run I've found you can be 5-6 gallons low and it makes no differecne in ET/mph what so ever.