In the last 8 years not much.
Last year we bought a new to us 2006 Sea Breeze.
We had looked at new ones before we went shopping to compare features and decide what was important to us.
The most important thing for any RV is floor plan.
The only new change we noticed seems to be less carpet and more vinyl/hard flooring. We wish ours did not have any carpet.
Other than that our 2006 has everything the new ones have.
Ford has not made major changes to the chassis or engine since 2005.
Don't worry about new, just floor plan, features,and condition.