I am in the process of designing a 2' x 4' CNC plasma cutting table. I have never used a plasma cutter, and don't own one as of yet. In the past I have used angle grinders and on complicated stuff I have had access to a CNC laser cutter.
I have a some used RV water storage tanks from an RV to flatbed conversion I did. The RV black tank is almost sized perfectly for my table and would be easy to use as it is molded to sit between the 2" frame rails of the trailer and is slopped for easy draining. I have cut the top off of it (see image).
Has anyone had experience using plastic for a water table? Would there be a problem with it melting the plastic by heating up the slats or the cutter piercing all the way through the water to the bottom? At its shallowest it is 2-1/2" Deep and the cutter would rest 2" into the table on all the axis, so it would not get near the lips of it.
I could easily put a sheet of expanded metal below the slats as well to catch the larger pieces that fall through (which might retain more heat). It would also make it easier for me to fish them back out. 
