We just bought this motorhome, it ran fine until I put gas in it. A mile or so up the road it just quit. A mechanic looked it over and agreed with me after I installed a new fuel filter that I probably had water in the gas , we found out that it sat in storage for about 2 years. I put in several bottles of dry gas, can I expect that after it sits for a couple of days that it should be okay. I put 15 gal. of new gas in on top of what ever was in the tank. It's a 1989 chevy 30 chassis conquest motorhome.

Water sinks, and rusts out the tank, as well as getting into fuel lines and so on.
I don't know why the mechanic didn't just offer to siphon it out then and there.
Drygas might be enough but it depends on how much water there is.