We went from a 32' Gasser in 2005 to a 36' DP. We didn't buy it because of it's length (fitting into parks), we bought it because we liked the floorplan and engine availability. We kept it for ten years and camped every year, including Yosemite and a couple of times at Yellowstone (Fishing Bridge Campground). We never had an issue getting into state and local parks.
Three years ago, we went to a 40' DP. We picked the Newmar Dutch Star because it was a true forty foot coach, had a tag (only coach 40' with a tag) and an engine brake. We live in California and I didn't want to deal with the additional licensing.
Our Dutch Star still fits in Yosemite and Yellowstone. We tow a 2016 GMC Canyon Crew Cab with 4wd. The total length is 64'. We've found that on occasion, when we call to make a reservation, people get a little weird when you say you have a 40' coach or larger. When we call now, we tell them it's a 39'. It's a mental thing.
So......don't be afraid of the longer coach, including a 45'. You'll be spending a LOT of time together and a larger coach can give you a little separation and a feeling that you're not closed in. Since you're full timing, you have plenty of time to plan each trip and find a reasonably priced campground near your destination.
You may also want to check for storage and weight issues. My 40' with a tag, loses 3' of storage bay, but has a pretty much unlimited carrying capacity. So look closely at the actual storage capacity when you look at different sizes. Typically, anything over 40' gets a tag. So.....if you bought a 40' non-tag, you'll end up with two more feet of storage bay, than a 41' with a tag.
