I think if you're gonna keep the truck a while, which I would and it appears you will, you'll have eco-modding thoughts about it in the future and if you're contemplating a temporary shell now, you'll do so again. It makes sense to invest in a permanent shell now and let the trip start paying back that investment in fuel savings. Having a shell is very handy, even more so if it's a cheap utility type that you just clamp down when needed and leave on sawhorses the rest of the time.
Camper Shell (Topper) $60
Dallas Craigslist, it's sitting on a longbed old body style F150 in the pics