The distances Bill mentions are achievable providing the terrain is reasonably flat since the towers in Houston are right at 2000', so that makes line-of-site to you just shy of 70 miles. This situation is where the Batwing shines over the Jack: extreme fringe areas. If you don't have a Wingman, add it. You also might be able to add a preamp, but the amplifier only amplifies whatever is at the input. No input, no output, so the highest performance antenna is a must. As for amplifiers, Winegard SensarPro is the best one out there for RV use because it has adjustable gain (sometimes too much is a really bad thing).
Look around and see what the neighbors or local ranch's have. If they are running 50' masts with giant wedge antennas then you probably won't have much luck 15' off the ground.