In Seattle, there is: Friendly Foam Shop
We haven't actually used them but they are highly recommended. I've been told if you order a RV, you should tell them to skip the main mattress and have your own made, that it will be better quality and likely cheaper but I don't know that from experience.
Ours is from the dealer's lot and has a memory foam mattress. We use a latex foam mattress at home so I hope they sleep pretty much the same, although the Sunseeker feels a bit softer.
Ohh I've been to Daytona once, beautiful!!