Former Neighbor has a tank in his truck bed. Holds one hundred fifty gallons, if I remember correctly. The 29 gallon tank, in his truck, isn't much when pulling 14 to 20,000 lbs.
There are stretches of road where you would run out on the 29 gallon tank.
One is from Russeleville, Ark area up into Missouri. It use to be an over 200 mile stretch of road through the mountains.
When you left the Su the stretch of road to next fuel use to be a very long way, almost to Wawa. Things have changed, perhaps, with fuel availability.
There are stretches out west where it it is over a hundred miles to next fuel.
If we ever get another coach I'm going to look for at least 150 gallon capacity and hopefully 200 gallons. Been considering another tank underneath this one. Weight and other problems might forestall one. It would be good to carry as much fuel as possible when it is 3.34 to 3.47 at some stations here versus over 4.0 in Michigan and elsewhere.