OK not knowing the dates or how long you have I'll set out a typical trip for us.
1) I-75 to I-10 then west.
2) San Antonio has the Alamo which may be worth visiting. You don't want to pull your RV on the San Antonio surface roads. We stayed at a CG just outside the city. Besides the Alamo there is the River Walk and a old Mission all in the same area. I promise you that you'll be surprised when you actually see the real Alamo.
3. OK this is where the time of year matters, if it isn't the summer then you may want to consider a side trip down to Big Bend NP and Terlingua. We went last time for a week in July and while we had a good time even being from Florida didn't help with the heat when we were back at the CG.
3a. Assuming you skip Big Bend proceed west on I-10 until you get to Hwy 54 at Van Horn, Go north there to US 64 and continue north. You will drive thru Guadalupe Mts NP. You can only drive around the edge of the park and seeing more means getting out and hiking. We've never been there in cool weather and those mountains look mighty hot in summer.
4. This brings you to Carlsbad Caverns, a must see. There is a CG outside the gate at White City but we've never stayed, we go into Carlsbad (town) and find a CG there.
5. Proceed north to Artesia and then west on US 70 to White Sands NM. Then west to Las Cruces. Then either continue west into southern AZ or go north on I-25 which will eventually bring you to where you can head to the four corners area and the major parks-Mesa Verde, Canyonlands, Arches, Capitol Reef, Bryce Canyon and Zion and a lot of smaller parks. That comprises the "Four Corners Loop" which many people take as their entire vacation.
5b. Going west instead will bring you thru southern AZ and eventually into California. Adding California will add a -lot- of time to your trip if you do King's Canyon, Sequoia and Yosemite. Frankly I'd save those for another trip that would take you north thru those and Lassen Volcanic. the Oregon and Washington coastline highway, Crater Lake, Mount Rainier and Olympic National Parks. You can drive west from there to get to Glacier and down to Yellowstone/Tetons. Even if you visited Yellowstone before one trip isn't enough.
6. When you finish the four corners go north to Yellowstone/Tetons
I'm skipping many smaller parks which you may want to stop at depending on your schedule. Parks like Petrified Forest, Chaco Canyon, Natural Bridges, Monument Valley, Dinosaur NM, Devil's Tower and probably 30 or 40 others.
Give us a better idea of what RV you have, what time of year and how long you have. What I set out above is 6 weeks to 2 months minimum. More if you take your time.
