Definately the truck with the cap. I have done the flat bed cover and the shell and the camper shell is a huge bonus for storage especially with horns. A half ton truck will work just fine for your trip but you will be happier with the truck that has the cap.
I would not go to the higher magnification. Lots of mirage as the temp warms up and you will not be able to go to the higher magnification anyway. Another consideration since you mentioned hunting on foot is the weight. I would pick a quality scope in the same power range you have now and not...