I just went out for you and the best I could come up with was 81" and that was measuring from the floor to the top of the roof and then adding 3 inches for the fin. RAM says the height for the RHO is 81.9. The problem with trying to measure using the garage opening or using the ceiling height to the top of the fin is that there is some slope to my floor. You would really need a laser setup to get a truly accurate reading. However, if your opening is 83 1/8" it looks like it will fit, as long as your tires are over inflated or you have rocks stuck in your tire tread
Hope this helps.... and maybe someone can get a more accurate measurement.