I'm torn on sizing my caddy.
I think the tank on my tractor is like 18 gallons, and I've been using two 5 gallon jugs which have poorly sealing caps and require I hold them above a funnel shoved in the filler neck which is over my shoulders when standing on the ground. Since I have weeks of stump grinding in my future, I think it's time to eliminate this part of my work flow.
I'm going to make it have an integral skid base so I can use my forks to take it in/out of my truck's bed, but I don't want to store an excessive amount of fuel either. Too much open "air" inside and you get condensation - there in lies the rub... What's a happy medium?