Your PACK will use "large" size trays, which is easy. Try primarily Battlefoam 2.5 inch Terminator 35 trays. The cutouts are the perfect size you want. I have a PACK 720 with a PACK Plus zip on bottom and that's what I use. These will fit almost any of the new plastics easily. The only ones that are iffy are Turkina, Stone Rhino, and Longbow, they'll fit but they're snug. If you have a metal Ares or something you'll want a bigger cutout, too, so I just got one of the 2.5 deep Battletech specific ones with the five larger hex cutouts for the big stuff, which is plenty for me. The rest of mine are the Terminator 35s, they're great. I put everything from mechs to vehicles to infantry in them. Each tray is roughly equal to a battalion (three companies), which is cool for painting and factions, too.