Hi John,
Any unvented heater that burns any kind of fuel is going to put moisture and CO2 into the cabin.
I have a vented Force 10 bulkhead unit that burns kerosene, and coking of the burner is a maintenance issue. The same unit with the diesel burner is worse from this standpoint, while the similar unit burning propane (which a friend has) doesn't have this issue. I think my unit is rated at 8000 BTU, and warms the cabin of our 30 footer to about 15F above ambient - the difference between frigid and cool!
Since you already have the Honda 2000, the simplest solution for you would seem to be an electric ceramic heater. It won't be too efficient though. The Honda will only convert about 1/3 of the fuel BTUs into electricity - the rest is waste heat.
How about wool socks, gloves, and long johns?

Al