Maybe it was just my particular circumstances, but I booked a Junior Suite on FoTS this past January. After I paid my balance and a week or so later, I was given the opportunity to Royal Up. I was doing a solo cruise, so I checked with my TA and she said that since I was cruising solo, whatever I bid would be JUST for me and she said that they had verified that through RCI.
Unfortunately, that proved to be not true for me. I bid $300 for a GS. They accepted the bid, but then tried to pull $600 off my card. At the time, I didn't have that much room on it, as my bill was due in a couple of weeks anyway, so I ended up not getting the upgrade (which wasn't so much of an issue, as JS proved to quite sufficient). The point is, for me, anyway, it seems that whatever I put as the bid, it is based on Double Occupancy, even though I was cruising solo. I don't know if that is a change in policy, or if that is the way that it has always been. I don't really see that detail delineated anywhere. My TA was surprised too. (Us solo cruisers can't seem to get any love! ) Anyway, YMMV, but something to keep in mind.