My guess is a collection of small things such as a special interior color that can be used by the dealers as a way of not having to compete with someone else's trailer.
"Oh we sell the "Northwest Package" therefore the other dealer with his plain trailer isn't selling the same product, that's why ours is more expensive"
I see this a lot at the local "big box" RV dealer here. There really is no significant difference in many cases. It's a marketing thing and a way to negate competing with the other guy.
Just my guess...