Originally Posted by Scooternj
DOT guidelines are generally for commercial operators. Some states have their own guidelines, like Texas mandates only 3 tanks per vehicle.
As long as you follow common sense (i.e. strap it down upright inside the vehicle), and have at most three portable tanks to rotate, you should be fine.
That's good advice. When I searched it out a week or two ago all I could find is that "common sense" seemed to be the main DOT regulation when total weight of LP and tanks is less than 1000 pounds. I think there was something about it being carried in a place sealed separate from the driver compartment, too -- in a part of the vehicle open to the outside, like a truck bed or under-body, meets that requirement. I can't speak to whether states might have their own additional rules.
As far as undercarriage mounting: I wouldn't even think twice about carrying a cylinder in a rack, or in your shiny new belly bins, especially if it has its valve closed and no hose connected. It has to go someplace and "officially" it can't go inside with you where it presents asphyxiation and explosion hazards if the valve leaks, so an under-floor cargo compartment is really the only choice.
When I did my 10 day trip two years ago I had one 20# cylinder inside the bus stacked among some boxes so the cylinder couldn't go rolling around. I set it outside and ran the 10 ft hose through a window when we needed to run the propane space heater, water heater, or camp stove. Not great, and won't do it that way long term...
Three cylinders may be more than you need. 20# will run a propane stove a long time.. maybe enough for the whole trip? It's not all that hard to find a place to have your one cylinder refilled so long as you think of it during 9-5 business hours. Exchange costs more, but is available 24/7 if you're in a bind. If the generator is "just in case" then I wouldn't worry about bringing a ton of fuel just for it.