Rwilly, I avoided doing a panel glue up for the bottom; If I did I would then want to go back and cut slots or drill holes for air flow, so instead I cut slats and mounted them in a rabbit. They are held in place with brad nails (from a staple gun) put in from the sides horizontally. I did a rabbit as opposed to a dado to maximize the inside depth of the drawer, and give the drawer a flat bottom. The backs were attached with a rabbit, a dab of water proof glue, and some brads. There is a picture in post #17.
Glue should be enough, I would think. The brads made it fast to assemble. One note; I did most everything in 3/8” thick SC. This stuff is flimsy like balsa and I wanted some strength for the size I was building. The drawers were about 13” D x 16” W x 3” H.
If I were doing a large tray, it would be all slats, with rabbits on three sides of the sides – none on the front, back or slats. All 3/8”. For a small tray, 1/4” SC, and I would forgo the rabbits and just to but joints. I would use glue and brads on both – “suspenders and a belt”.
Good luck with the trays – you should post some pictures.