That is almost a perfect cube, as well as flutter you will have standing waves, don’t bother with foam, get about 12-18 mineral wool broadband panels, don’t bother with bass traps either - they will take up too much space and won’t be very effective anyway.
Use small front ported or unported monitors, 5 inch driver or less, proper placement and a decent set of monitoring headphones for checking bass. Keep monitor levels at about 73db and get a spl meter to ensure you can set the level correctly.
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