On our redwood, the spare was up under the 5'er and it was the filthiest thing on the rv with all the road spray and dust
FYI - I too have heard (and seen) pros and cons about bumper mounts.... years ago the squar bumper was a massive piece of steel and could tow/hold a lot... but nowdays - not so much !
Was following a buddy in his brand new 5'er that had the oem spare tire on the rear bumper and watched it twist and almost fall off in front of me
the factory welds were not good enough for that. much less much else...
if you still want your new rv frame warranty, I would get some written correspondence from the factory before doing anything (JMHO !)