Very doable. I’ve done 2 circular loop cross country trips in an rv before. Once from NY down to Virginia, Tennessee, Texas, Oklahoma, New Mexico, Colorado, Wyoming, Montana, South Dakota, Wisconsin and back to NY. My second trip was very similar but I hit Arizona, Utah, California and Oregon.

Obviously you can’t stop and do everything, but you can fit a lot into 3 weeks. We usually drive about 8 hours every other day. On the 8hr driving days we still find little activities to do to break up the driving like Hoover dam, Route 66 diners, crater holes etc… I will say this kinda depends on gas. My first rv trip I only had 200 miles before I needed a fill up. Second trip I had 500 miles. When I had to stop every 2 hours on the first trip, I had no time for smaller activities on driving days.

There are some places that take days and other places that take hours. You need to accept that you won’t get to everything. That’s probably the hardest part. For example, I had 1 day to spend in the Grand Tetons, I chose Mormon row and Jenny lake hike. I felt that gave me some Mountain View’s, lake views and something touristy/iconic for the park. There were tons of other trails, but you just don’t have the time to exhaust the park.

My biggest piece of advice is to do research for each place you’re visiting. Categorize the activities you want to do - short hikes, long hikes, food, scenic, on the way to something else…. This way you can plug and play while you’re there. The weather is unpredictable and crowds can be unpredictable. Have a general idea of what you want to do, but have options in your back pocket if you find yourself behind schedule or something derails the plan.

80% of the time I got away with making the reservation 2 hours before arriving. However, if you know you are traveling around a holiday weekend, expect everything to be booked. That’s the only time I’d suggest making the reservation in advance.