Just Lee,
Before you go to Lajitas you need to visit Alpine and stay at the Lost Alaskan RV Park, be sure to check out the area. It looks like you RV in a Motorhome so please be aware that when you travel to the border you will have to go though a Border Patrol Check Point on your way back up from the border no matter which route you take, about 20 miles north of the border. They can and sometimes do enter your RV with their drug dog and they also look for weapons, so if you have weapons keep them out of site and don't take any drugs with you.
Apart from that you should go over to Marfa, TX and down Hwy 67 to Presidio and connect to Hwy 170 East toward Lajitas and on to Terlinga and then to Big Bend which there is a State Park and a National Park. On the way keep your camera at the ready, you will see some beautiful scenery, such as the Tee Pee Picnic Area, Fort Leaton State Historic Site, Beaton Warnock Visitors Center, and play Golf at Lajitas Resort. Don't worry to much about the heat in May, it really gets hot in August and September.
Google: FM-170 The River Road and www.wisewife.com The River Road.
Take your time and have fun, take I90 over to Del Rio and then north to Houston.
Good Luck.
Bill-Edna
The Boys-Beau & Jacques
:C2008 F450 DRW 6.4 Diesel SDCC
:C2008 Fuzion 373 39' Toyhauler
Keep the Shiney Side Up
Dull Side Down
Don't Smoke The Tires
Stop and smell all the roses as you travel this Great Country.