On my boat I have an Espar diesel heater. Works great, but they are a lot of money.
Company in Russia copied them, and sell them for about half price. Fast forward: Company in China has copied them and sell them on line for $225.00 plus $5.50 shipping. I took a chance and bought one. It actually works. 12 volts for the electrical system. So I bought a new battery for the belch mobile, and a battery tender. Unit comes with a tank for the diesel. The instructions are crap, but they are pretty basic to set up. Press the control button to start, press again for about three seconds to stop. Heat is not instant, but quick enough. I drilled a 4 inch hole through the side of the rolling condo, and finally have some warmth at the chilly end. Later when the new cottage is built, I will use it for the workshop. Hate to give a plug for Chinese junk, but sometimes it works.