I would steer you away from any sort of tray.
Get yourself a decent - 12" Diameter - sized Stainless Steel Mixing Bowl. You want to get both hands in there and mix freely and casually, without tabak going all over the place.
This will help to ensure even dispersion of all the ingredients in your mixture, easy to work with; AND, the tabak STAYS in the mixing bowl.
Stay away from a plastic bowls, as static electricity will build-up and you'll spend time trying to pick all these little tabak flakes off the sides of a plastic bowl. - Sherm Natman