I think the idea of 2 crewmen to each quarters (aside from perhaps higher ranking ones), would be not only practical from a space-aboard-ship standpoint, but also from an RP perspective. As you said, having crewmen “bunk up” would give some great opportunities! Complaints about the other’s use of space or messiness. Or even some food that they bring aboard that might be offensive to the nostrils! Or maybe if they’re pals they could throw in some inside jokes about a prank they pulled. 😛