So to follow up on this story. I couldn't do a two-reservation method since I found out that making an award reservation through Chase Ultimate Rewards meant it was a pre-paid reservation. I couldn't get any credit for the rental days nor could I do much to modify it except through the travel agency Chase booked it through.

So lesson learned is that if I want to book through Chase Ultimate Rewards, I get what I booked for.

When I got to MCO, I don't know what side (A or B) I was in, but the agent told me to pick out a minivan from the Aisle, so I think I could've gotten a free upgrade if I booked a midsize. There were quite a few minivans available that night, too.