for what it is worth....
My set up - 2001 Chevy 2500 HD diesel short bed towing a 2007 Montana 3000RK. Got the truck used in 2007 and like the OP, mainly just use it to tow the monty. NOW, I take the truck on a trip at least every 2 weeks. About 3 years ago, when towing got a check engine light and reduced power mode. After the trip found that sludge build up in the tank led to problems with the fuel injectors and the seals which cost $6500 to fix. Don't use additives but doe run it to mix the tank contents up and keep fuel from staying around too long. (fill up once every 2-3 months depending on number of times we took the monty out.).