We have a 26ft TT and have found that this is the maximum length we would go to in order to not only fit into state and federal park campsites,but to navigate the roads and back into the sites.Now a 5th wheel is a little different and you could go a little longer than with a TT.But I would stay around 30ft.Once you go above that,you really limit yourself to a smaller number sites you can fit into.And for us,we like to have that ability to choose a more isolated site when available.