Vic, I would think if you stayed close to a 32 ft 5R you most likely won't have a problem, even with the older parks. Most 5R's now have floor plans which offer 3 or more slides so the length is not as important as it once was regarding living area. Call some of your favorite parks and talk to the manager about large rigs and see what they have to say, after all they would know best what problems they have experienced with them.
Also, I have a slider and have never found the need to use it, even in tight hard to get in spots.