Insurance from MBA Insurance is something you should look into. They may have some pretty steep requirements but are "the" insurance company in the RV Rental Business. They require the renter to pay for the insurance on a per day basis.
You may also consider looking at the larger rental sites for ideas on deposits, rules, miniumim and rates (www.elmonterv.com
). I think you have an opportunity for a premium rental with an Airstream but could be somewhat limited in available renters based on a renter's tow vehicle, hitch setup, etc.
Have you considered renting it in a stationary format? Kind of a semi-permanant arrangement where you tow the AS to a campground then rent it like a cottage? Obviously you would need a campground willing to participate with this transient concept. But you gain the benefits of lower chances of accidents, open up the pool of renters to people who own cars or smaller SUV's and get 24 hour monitoring from the campground.
Please keep us posted on what you find as I'm sure some of us have considered the possibility of renting ourselves.