Now I have a question. If you have a park model, doesn't it already have a gas/electric water heater? I'm not convinced the tank less systems are all that efficient. You also need to determine the power draw on the tank less system you are looking at, and make sure your power center and electric cord can handle it. If electric was included in the site, I would use the electric side of the water heater. If it is 6 gallon, (I doubt in a park model) I might switch it out for a 10 gallon gas/electric. Good luck and I hope others comment.
Also the vin should be stamped on the tongue, and might be on the weight sticker inside one of the cabinet doors. It would also be on the registration, if you have plates on it, the title if you own it, and if all else fails, look at the bill of sale.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT