As others have already said, unless you have stains, completely stripping the "old" wax off is just extra work.
That being said, I've found using Dawn dish soap does an excellent job of stripping wax off... I've used it to wash both my motorhome and boat before reapplying a fresh coat of wax.
As for stains... my wife saw me scrubbing and scrubbing on the back of the MH one day and suggested I try a Mr. Clean pad. AMAZING!... it cut through the stain like magic. though I ended up having to use it (actually an entire box), because they left super clean spot where-ever I'd used it.
Best of luck... it's a big, really big, job, but worth it when all done.