Why do you need an iPad for camping??? Isn't the point to get away from technology? In any case, if you're out camping, getting coverage may be a little tough depending on where you go. I linked the coverage maps for 3G service. If you're out camping, don't expect to get 4G. You'll most likely have 3G service unless you're in a remote area. You'll see with Verizon you will have a high density 4G coverage when you are in a metropolitan area. Once you leave that area, you will be on EVDO. With AT&T, you'll have 4G only in areas that are shaded dark blue. To tell you the truth, both networks are about the same in metropolitan coverage except Verizon tends to have higher reliability. Once you're out of the metropolitan areas, you normally get 3G and even further out, you drop down to EDGE which is rare if you're driving but if you're camping, wood is not the best material for wireless signal to go through.
http://www.cellularmaps.com/3g_compare.shtml