Motorhome Length Limit?

We have a 40' motorhome (without a tag axle & no problems) and our first choice is always a public park. Honestly, we have never chosen a park that we couldn't fit. Just do your homework and you'll find "quality" sites. We've found them - without making reservations - in Glacier, Yellowstone, Grand Teton, Zion, Rocky Mountain among many, many others. We also find gorgeous sites in the national forests. No, you won't fit in any site but you will fit in a lot of them. As stated, pull in late Sunday through Wednesday for plenty of choices. Also remember that when a reservation system says "full" that typically doesn't mean that there aren't sites available that are not on reservations. Have fun!