When visiting Venice, we stayed on the Sabbioni Peninsula just East of Venice, and took the ferry into town. We were the only tourists on the ferry early in the morning. It was much cheaper than trying to stay in Venice, and it looks like there is camping available according to Google Maps?
On another trip we took the causeway towards Venice from the NW, and got absolutely the last parking spot on the top floor of the multi-level parking garage. I had to crawl out the window to get out of the car… an RV would be impossible? I actually had to cross the causeway 3 times. I dropped my wife and luggage in Venice, and then tried to return to the parking garage, but the left turn access was closed, so back across the causeway, meander around an industrial area, and finally back unto the causeway and into Venice… it took 45 minutes. There was wine with lunch.