Personally if I was looking to do something like that, I'd look for a plastic flood table tray that most closely fits the bottom of the tent. My impression with almost any tent brand is that the trays they come with are designed to catch and contain the occasional medium-big spill and the day to day little spills that happen, but not really much heavy duty beyond that. May work for it, but better off with something designed for that kind of duty I would think.
One other thing to consider. If you use a single, large tray and moldy or otherwise nasty stuff does start to develop you have to take everything out to get the tray out to clean it. Versus just removing the pan style under individual pots. *shrugg*