ABS can be easily stiffened by heat forming a few channels using nothing more than a heat gun and scrap wood or even reinforcing rod. I've been recently working with it extensively on a car with all ABS body panels. It's easily obtained through any Grainger or Mcmaster. Call the local branch for availability. If it cracks or breaks it can be repaired with more ABS and MEK solvent.
McMaster-Carr
Search abs sheet - Grainger Industrial Supply
Sweet pan! I might just do the same thing.