A tip from my Air Tractor experience for you guys with full length tanks...
...was learned at our NAAA (Ag av meeting) meeting in Reno, last December.
Leland Snow told me that regardless of how they configured the different tank options on Air Tractors, the dealers always had a customer who either wanted more fuel and sometimes, less fuel, so they ingeniously solved that problem:
They built large tanks that go most of the way along the wing, between spars, but about half-way, put in a solid, barrier rib with a pipe plug in it that you either leave in ,for smaller fuel capacity, or remove via an inspection plate on the top, reach in and remove the plug...voila!!... double tank size. Re-proseal the inspection plate and re-install. I thought that it was a pretty trick solution to an age old problem and something you 'Round-the-worlders' might appreciate.
You'll then have an inboard fuel cap and an outer one for when the large fuel capacity is needed.
This way, when you get done with your trip and don't need that much fuel out there, put the plug back in and have smaller tanks.
Best,