I don't know about Ford or Ram, but GM puts the larger 36 gal tank in the crew cabs, including 6.5ft bed models, but just the 25 gal tank in extended cab models. Since the crew cab is only 9 inches longer and still fits in my garage, it was an ez decision to go with the crew cab.
But you also have the option to replace the factory tank with a larger aftermarket tank from TransferFlow or Titan, both are around 50 gal. I had one on my previous truck for 10 years w/o issues. Some do tow with just a 25 gal. tank, but that is not my preference, even willing to spend more money to get the tow vehicle set up the way I want it.