Whatever you get, get something "hefty" now with this purchase. That way, "when" you change campers and tow vehicles (an you will!) ... you've already made the investment and won't have to re-do it to go heftier if you go minimum now. Just my advise!
I do think most push-in-out sensations coming from passing semi trucks is because the tow vehicle is too small. Same trailer, same weight distribution, but a world of difference when towing my 18 foot Dutchmen Sport with my 1500 Chevy Suburban, and then we changed to a 3500 duly (gas) Chevy. Never had that push-pull-again ... there again, same trailer, same weight distribution hitch. Just my own experience speaking here. Your's may be different.