I used to have a portable catalytic - used in the boat yard in early spring. The moisture was so extreme that it made the thing unusable.

I have a Force 10 propane heater aboard and use it quite a bit. It still adds some humidity - even though it is vented but it works well. A fan right above the heater helps move the heat around.

The downside of propane heat is the speed at which you go through propane. I can empty a five gallon tank in three days. In BC this last fall we went through at least six refills. Fortunately, it wes very available due to many tourists with trailers up there.