Thanks, gents. They are 16" steel.
Some background: I need to have the inner rear looked at, as after I got the unit home, I went to check the tire pressure before I took it up to the storage facility. I assumed (bad move) that they checked the pressure before I took possession. I checked the front (from the way the covers were aligned there was no way they checked) and found them to be at 60 vs. 75. When I went to check the rear, I put the gauge on and the valve wouldn't close. Not a happy camper at that point! I kept trying to put air in, but it didn't take. In a bit of a panic now, I put the cap on to minimize the air loss and took it up to the local tire place. He had a hard time taking the valve out and replaced it, but even the new valve would not take air. He had to pull it, add air and then replace. Doesn't seem to be leaking now, but it sure concerns me. I purchased this new a few states away, so I'll need to take this to either a local Jayco dealer or a Ford place.
Funny, but I called Ford and they said they'd send someone out to replace the tire, but as I had no tire to replace it with... figured it's best to add a spare.