IDE say it's a toss up. I would buy in FL and do your cross country and west coast trip. Then see how quickly you could sell it in the Seattle area. Keep in mind if you try to sell quickly you are going to sell for a lot less than you paid for it. For the loss of money on a sale I would have it shipped back home.
The last thing you want to do is buy an RV mid trip and discover it has issues. That's why I would buy before your trip at home and use it in the area to figure out its quirks and if it will have issues.
Just curious, why are you not going to drive it up to Alaska?
