I agree with the idea of getting her used to the TT. Right now, she gets all excited because you're taking her some place. Then you get there and you leave her alone in a strange place.
First, just spend time in the TT while it's parked in your driveway. Give her special toys (if she likes them) and/or treats that are ONLY given when she's in the TT. Let her look out the windows and get familiar with it at home. Make it a special treat to spend time in the TT.
Then, take a few trips where the focus is to spend time WITH HER. Hang out at the campsite, take walks with her, etc. Let her get used to the idea that the TT is your home away from home. As she gets comfortable with the TT as a home, make short (2 minutes or less) trips away without her - use the campground restrooms, take a short walk before dinner, etc. If she does well (no barking), then try a slightly longer trip (up to 5 minutes). If she does well after a few times, stretch it a bit longer again; if she gets upset, go back to the previous time frame and start again. Keeping extending the time away in increments and go back down a step if she falters at any point.
Don't make a big deal about leaving. Just tell her to "be a good girl" and leave. You can give her a toy or a treat when you leave. But no hugging, cuddling, etc. When you come back, give her lots of love (if she behaved).
I wouldn't go to medication as the first choice. Medication won't change her reaction to being left alone, it will just block the reaction. It's always better to change her reaction to a positive one.
P.S. I did the above with my dogs when I got my first TT. We since switched to a MH. They both LOVE their clipper and can't wait to go places in it. I can leave them alone in the RV for a few hours as needed. One thing I do make sure of doing is to have trips that do not include my leaving them alone for much of the time. We do real camping trips and they swim and hike and hunt lizards and just have fun. Those trips seem to make the others more bearable.