I own the 400 series cambros. You can put 4 full 6" deep trays in there or if you don't mind stacking, you can fit 6 full sheet alluminum trays. I do this when I have rice or tri-tip. I just fill to the rim of a tray and cover with foil, so that there isn't a mess at the bottom of the trays.
Those 400's do get heavy, best loaded and unloaded by two people when they're full.
Diamond Plate FAT 50 Ultra
55-Gal Horizontal offset
2 55-Gal Vertical Barrels
Anything worth fighting for is worth fighting for dirty!