If I were going to any place out west or remote I would have an extra in bed tank. If you had a 90 gallon tank plus your 26 gallons you would have a range of at least 1000 miles. Now that is piece of mind.
This is what I had. I could still put my slide in camper on the bed with this in there.
RDS Vertical Diesel Fuel Transfer Tank — 90 Gallon, Model# 72118 | Auxiliary-Transfer Tanks| Northern Tool + Equipment
They have a kit that lets you hook it to the fuel filler neck. This allows you to get around the EPA regulation of not hooking it directly to the fuel system. Filling up is a pain and many times they gouge you. Having the luxury of filling up when and where you want is priceless.