Followup on RVmattress.com. We ordered a 70x80 RV king but they will make any size you need. They stated that shipping would be by truck and kept us updated very well, even showing FedEx's truck location as it traveled I40 from Phoenix AZ to central NC.
I thought it would be a giant 6' by 8' box due to the truck reference, but a little FedEx van pulled in the drive and out came a 24x24x70 inch box. That thing was vacuum packed and rolled up in a bag.
That made it easy to get into the 5er. I cut the bag with a knife and voila instant 8 inch thick 70x80 very comfortable mattress. Getting the old one out wasn't so easy. It was like wrestling an octopus. Total manufacture and shipping time exceeded the quote by a few days but hey, these are unusual times.
Again, I have no connection to this company.