Bought our first pop-up tent trailer in 1988 and have owned three pop-up trailers, a 28' Sunline travel trailer, 26' Winnebago Minnie trailer and now the 2012 Bay Star motorhome 9 (gas engine). Every rig we've owned has been perfectly fine for traveling 400 miles or more per day. But, you do adjust your traveling style based on what you are towing. Back in the days of the pop-up trailers and traveling with our two sons, you had to find places to eat and rest rooms. With travel trailers, you can stop and use the trailer, but with some possible restrictions such as having to deal with slide-outs blocking the walkway. A motorhome makes it much easier to pull off into a rest area, use the bathroom, have a meal, etc.
Another factor is how often you have to stop for gas. When we pulled the Winnebago with a Tundra, which had a relatively small gas tank, gas stops were required at about 200 miles since I don't like to gamble with a tank getting too low. With the motorhome, we can easily do a day's worth of driving but at our age, we never go over 400 miles in one day, and prefer to stay around 300 miles per day.
If $$ were no issue, the only change I'd make at this point would be to move up to a diesel pusher with a better ride than the F53 chassis ride quality found on gas motorhomes. And, if we really wanted to do 500 miles a day, I'd either move up to a diesel pusher and consider a fifth wheel trailer with a nice truck.
