You will probably get about 1 gal of water per 1 gal of fuel used.
Unfortunately dehumidifiers do not work well when its cold, so this can be an issue.
I tried putting the dehumidifier in close proximity to the heater to dehumidify the warmer air. It works decent, but a good dehumidifier uses a lot of energy. When you combine the cost of the propane & the cost of the dehumidifier, an electric heater may be less grief & similar in cost.
The more temperature variation you have, the more prevalent the moisture problem is.
Before I had permanent heat, I used a torpedo & although it warmed the space, I had to open all doors at the end of the night to relieve all the heat & moisture, otherwise it "rained" in the building overnight when it cooled off. There would be frozen drops on everything in the morning.