$100 for used?
That's just plain silly, it would kind of stink to find that you paid for it then installed it to only find out that the control is bad or it has damage to the tank that was hidden.
pony up for a bit more money and buy a new one, much better than fooling around with a used one that in many cases will need some TLC.
A new 6 gallon Pilot Atwood is not all that expensive..
You can get one
HEREfor $265 US..
Alternately since you are talking about a Park model, perhaps consider buying a small home 120V electric tank instead. Granted you may need to upgrade your electric panel if it is only 30A but in the end might be well worth it.. 10 gallon 120V 2Kw electric is about $290 US at Home Depot
HERE