I have a older Deb, 1960, with the 2, 25 gal mains, and 2, 10 gal aux tanks. I have 63 or 64 gal usable. I considered tip tanks, and they would be nice, but not worth the extra cost for me. After 3 or 4 hours I’m ready for a break.
The newer ones have two 40 gal tanks with I suppose 74 useful.