BigSkyRoadGlide: I have a 2021 Ram 2500 Power Wagon. It comes with a 31 gallon tank. There is no upgrade available from RAM. For my purposes, off road, remote places with no cell coverage, no gas stations, no electricity, at 12 MPG, its just too small. I carry two 20 liter NATO (= 11 gallons). And I'm glad I do. I came out of the North Maine Woods at the end of the day with about a third of a tank and planned to gas up in the morning. Unfortunately, the power was out in the morning so the closest gas station with power was about 30 miles out of the way (60 mile round trip). We ended up using the jerry cans and all but about 2-3 gallons that day, but I didn't have to waste 1.5 hours gassing up. I'd definitely love to have an extra 9 gallons. Given the cost of installation on top, I'd probably opt for a 50 gallon take for the extra $400. That's only $40/gal. Really, I just wish RAM would offer a 40-50 gallon tank option on the Power Wagon.