How long is a particular contingent aboard. Since they don't conduct shipboard operations, familiarity with a specific vessel is not relevant and there is no adverse impact in them having short tours. They could be rotated in/out on a garrison system, spend a week in jump and then deploy. After deployment they are picked up and delivered back to a garrison system.
To my mind barracks are bunks, ablutions and some messing facilities. 1DTon per marine is still 14 cubic metres. That might appear cramped, but sounds positively voluminous compared to some service accommodation I have seen. Subs are pretty cramped and you also don't get to go on deck with them. At least star ships can rotate crews out each time they enter a system, many of our subs don't get to stop.
Boredom would be the biggest issue, but that is true of anyone during jump. Sensible officers will use this time for sim training etc (which can be pretty compact). Armouries, combat training etc. are different facilities that you might wish to include if you intend for marines to be a permanent contingent. Marines might also commandeer cargo spaces for recreation if they can get away with it, but PT doesn't need lots of space, most Gyms are pretty cramped.
If you spend much of your time in a battlesuit you are not really going to be the claustrophobic type.