On a cross country trip several years ago the bumper mount fractured and I nearly lost the spare. Since then I have yet to see a bumper mount that doesn't make me nervous. When we passed through Elkhart I went to the Nexus factory and in addition to having them add an extra seat belt in the coach I had them build a permeant spare tire mount under the rear of the coach.
Sorry, I don't have any pics but they welded a framework out of which a threaded rod comes down through the tire and a steel bar runs athwartship that the tire snugs up against. You just loosen the nut on the threaded shaft and the tire drops down and out. Yes it is a PITA to wrestle with but that is what the ERS guys are for... at least I have a good spare mounted on a rim ready to deploy... which came in very handy last October out on I-10 when my outside/driverside dually grenaded.
:C