There are two things that could be a big problem there for you - fumes and CO build up if not adequately ventilated - and propane creates water - which is not very conducive to a good paint job.
I bought some fence paint late last year, and I was told that the Blue Base was the most expensive.....just what I was told. It cost almost as much for the blue base, as the rest of the mixed colour - a 5 gallon bucket.