Good morning fellow cross country/endurance enthusiast. The longest endurance flight (that is remaining at the takeoff field for the entIre flight) that I have achieved is is 6 hours and twelve minutes non stop. The airplane is a much modified Senior Cadet with an extended wing by 10 inchs and carrying almost a gallon of fuel in three tanks plumbed in tandem and the power was provided by a lovely OS .65AX with no fuel pumps at all.
This ship is set up also with a single central float of considerable reserve bouancy for a 'dreamed' about flight over water.
I also a little over a year ago flew from Laughlin Nevada to Lake Havasu Arizona down the Colorado river with a Bridi Sun Fly !!! on twin floats also powered by a OS .65AX and this ship carried 72 ounces using four tanks plumbed in tandem in the nose and along the top of the fuselage from the firewall to even with the trailing edge of the wing, Agine no pumps.
The tanks that Dub Jett sells are called bubbless tanks as are the bubbless types that are called Tetra tanks all of these involve an internal bladder inside a hardshell case with muffler/header pressure applied between the hardshell and the bladder. These are wonderful tanks with great fuel delivery performance but also as you noted quite small and once you go beyond the largest Tetras become impractical especially when you trying to package as much fuel into as little space as possible.
I have always avoided wing tanks for the reasons you have noted and while yes the introduction of pumps would almost certainly be required and that's added complication I have preferred to avoid.
If you are interested I would be happy to post pictures of these ships and fuel systems
John
