I wouldn't think about doing a back seat without doing a full cage to protect the occupants. Even if i only planned on using it for putting around......it only takes one time to really hurt someone.
I got my rear seats and cage from Brian(Evo) at Long Travel Rhino. It's a little pricey but well worth it to have the piece of mind that if for what ever reason you ever do roll the thing...you want be hurting or killing someone you really care about, precious cargo IMO.
I could not agree with you more, and again, your Rhino is sick.