I have it figured out... I think.

Two 12 gal. Miller fuel tanks tied together and using a lawnmower gas cap fuel guage. The cork on the guage would give adequate readings and seeing it doesn't go to the bottom of the tank, it wound have plenty of reserve when the guage actually shows empty.

And instead of dual batteries, I'll use an engine battery and throw in my thousand amp jumper pack. It charges via a cigarette lighter and you can use the same outlet for accessory power. It'll be tucked up in the poor excuse of the cabin with the small cooler. The jumper pack will reduce weight and valuable space.

Though compact, this should allow plenty of room for the wife and I to enjoy a long run on small rivers.
This is looking like fun in the making.