The chocobros have a system worked out for deciding the sleeping arrangements whenever there's only two beds: with card games! Three hands, with the loser dropping out each round until there's only one left standing. The winner gets his choice of bunkmate and bed, but really, the four of them have been collectively together since before the road trip started, there's not really any losers. Sexytimes optional, but preferred.

+ Prompto wins for the first time ever, but realizes he didn't actually pick somebody to sleep with and agonizes over the decision.
+ Optional rule: winner always tops (or tops from the bottom).
+ Ignis wins and uses it as an opportunity to be a little selfish and indulge himself with one of the others.
+ The two who lose the card game get off on watching the winners.