I think you have combined two different comments into one generalization. Many people feel that MH's are easier to use if you're going to be moving around from RV park to RV park since there is less setup time than there is for a 5er. But there isn't any reason a MH has to be moved frequently
Diesel engines, in particular, do not really care about sitting around for months waiting for their next use. Think about how many farm machines sit around waiting for the next planting season. Sure, if you didn't start them for years you might have issues, but a couple of months isn't going to bother them or the rest of the MH. If we're at the seashore for an extended period of time I'll put a few ounces of algaecide in the fuel tank, but that's all I'll do.