This article only applies if you already have a MyLTV account. If you're creating an account for the first time, please read this article.
Updating your VIN to your new coach is simple:
Log in to MyLTV
Go to the Settings page.
Scroll down to the very bottom of the page. There should be a section titled Bought a New LTV?
Click Update VIN. Enter your new Chassis VIN into the input box and click Update.
That's it! Your VIN should now be up-to-date in MyLTV.