I vote for the under-mount between the frame rails. This keeps it out of sight of potential thieves (although I suppose they may look under) and away from UV exposure. Changing one of these is not much different than a full size HD pickup. The rear axle will be heavier of course, but the tires are about the same weight and the lugs should only be tightened to 140 ft./lbs. A person of average strength should have no problems loosening or tightening with a standard 2 foot tire iron as long as some knucklehead installer didn't rattle them on with a 3/4" impact wrench. These are nowhere near as difficult as the 22.5s found on larger rigs, these are often torqued to 450-500 ft./lbs.
