Here's a link to Cheap Heat. If you have to pay a dealer to install it, the installation expense could be more than the cost of the device.
In terms of payback, it can be problematic because you'd need a lot of long-term stays to recover the cost of the device. In most parks, if you're there on a monthly rate, you have to pay for the electric separately. If that's the case, you'll have the convenience of not having to refill propane tanks, but you may not save much.