A 1/2 ton truck will pull your current trailer just fine, but definitely weigh the odds of you buying a larger RV vs buying a 3/4 or 1 ton truck.
It isn't on your list, but I'd include the Ford Ecoboost 3.5L V6 for a 1/2 ton truck. I had one and I liked it a lot better than the 5.4L V8 F150's I test drove. That Ecoboost has more torque and pulled better down low than the V8, to the point where the V8 felt like a V6 and the Ecoboost felt like a V8. And the Ecoboost gets good gas mileage.
If you decide to go with a 1/2 ton truck, might as well consider the Tundra and Titan.