Thanks for all the replies.
We want to keep AZ as our domicile for awhile as I am working here. The reason for Quartzsite is no smog check for vehicles registered in that county. While AZ will tax part of my retirement when we finally get there, the income will be low enough that it will not be a big deal. Having said that, we will probably, eventually, use a FL address.
Thanks again. If anyone else has some thoughts on mail services, I would appreciate the input.