dont need much...my buddy uses a portable propane heater in his...lol turns it on for a few minutes at a time. Dont they make one that will tap into your coolant line with a thermostate and everything??
A guy I work with uses a propane heater in his golf cart, has an adaptor that fits his cup holder. I've been looking at the ones that hook to the coolant lines, once installed I think it would be a lot more convenient and wouldn't have to worry about running out of propane or carrying extra bottles.
That's looks great, according to JC Whitney you also need Danhard Heater Control Kit - JCWhitney for new installations. I didn't see the control panel in the photo just the fan switch, did you something different?