It will be a long battle, but the first thing I would do is research how other ordinances of this type were overturned, copies of the ordinance and any petition etc that was used. (Sounds like you may have done some of that already.)
Next I would find out what kind of process is needed in your particular town to have an ordinance overturned, petitioned to be put in front of the council etc. Then get with a local attorney for assistance in the drafting of what ever the required document is.
Last get with as many RV owners in your area to either sign a petition, show up at a council meeting, to push for the change. Find the best spokesman to present your case in a respectful manner and hope for the best.
That's my two cents, hope this helps a little.
