Propane is dangerous to deal with. Obtaining the fuel, transporting the fuel, storing the fuel and making sure there are no leaks is critical. Everyone is familiar with how to plug into an electrical outlet and turn on a switch.
Propane is messy and requires the assembly of duct work from the flaming heater to the treatment area. This takes a long time and typically adds 45-60 minutes on either end of the treatment for set-up and tear-down once the treatment is complete.
Propane duct work is very intrusive, not discreet, blocks resident passageways and is a potential tripping and burning hazard if someone were to touch it (like an unsuspecting, curious child).
Burning propane gas introduces high humidity into the treatment area which very often results in wall paper damage and anything else that is glued together like most budget furniture and picture frames.
Most propane systems do not have automatic thermostats so monitoring the temperature of the treatment area is dependent on the folks running the equipment. Without constant human monitoring temperatures can exceed 185F. Electric heaters with auto-thermostats typically max out at 135-140F. There are many documented instances where too high heat has scorched wood, melted vinyl window blinds, blistered other items located in the treatment area and melted electronics like TVs.
Insurance claims associated with melting electronics, furniture, window blinds, picture frames and flooring can quickly outweigh the “low cost” of purchasing a propane system.
Some propane systems are even more dangerous and do not produce the heat in a trailer and blow it into the treatment area via duct-work but actually burn the propane in the treatment area or right outside the entryway. This is forbidden by law in most localities for obvious reasons. Please check with your local fire authority if this is the type of system you are considering.