We've tried the wax thing with OK results.  Recently I tried using a wax-based bike chain lube like White Lightning.  Goes all the way in between the teeth rather than just on the outer surface.  Downside might be it soaks a little into the zipper material.  It goes on as a liquid but dries to a wax sheen that covers all the surfaces of the teeth of the zipper.  A much smoother operation than just using a paraffin wax.  There aren't enough o's in smooooooth to describe how the zips work now.
As far as tires and blowouts, we never tow over 65 mph.  Even in Utah where the interstate speed is now 80.  Yeah, we're slower than many, but we stay in the right lane.