Sky, our Judson TNT burns 1.5 gallons of propane per hour of use at full rpm and propane heater at full blast. The heater is a #4 little giant high pressure unit.
Ive ran this machine for about 5.5 years, very heavy use.. its a workhorse. Maintenance is very minimal... basic oil changes, blower oil changes, pump oil changes.
Trust me dont go the ETM route, it sucks and your production rates will suffer while spending almost as much as a decent gas machine. I have an ETM sitting in the shop, ill never install it in another truck... ran that thing for 5 years and it was a pain in the ass.
This ETM had smoking hot propane heat the escape is just a portable that sits in your truck with a bigger waste tank.