You want something 2-sided for the back covers?
thought about 2 sided but honestly I would probably give myself a headache lining up both sides to make a single print as its not like page size.
I did some searching, wondering if a decent stock brochure paper will do the trick, will have the gloss I would be looking for. The matter then becomes making the tiny .25 inch type folds for the cases.
I have made a bunch for a few PS1 games using reg paper ive used for UCG but the quality difference shows, works well for UGC not for jewel apparently.