Instead of taking chances with fuel containers, how about using three DuBro 50oz tanks? They're 3-1/2" x 8-3/8" x 4-3/8", and 3 of them would be 1.17 gallons... still enough room to refill and drain the tank that's in the plane after the last flight of the day.
Two drawbacks...
It would have to be filled using the onboard pump, and at $12 each, it's not a cheap way to go... but look at the advantages:

We KNOW it's good for model fuels.

No risk of spillage even if the field box gets dumped.

Flexibility:
1 - Position any way you'd like so long as the clunk or pickup tube hits the low point
2 - Need more capacity? Add another. Only fly 1/2-A to .25 models? Only run one. Simply arrange them as you would a header tank setup... tank #1 vent to outside, clunk feeds tank #2 vent. Tank #2 clunk feeds tank #3 vent. Tank #3 clunk goes to the pump.

Personally, I'm either going to go this way, or go back to the original method. I need to check and see how well cans will fit now that Powermaster has stopped using jugs (some rumor of someone's very old, UV-exposed jug broke open in the back of their car).