I have not heard of joist lining before. But that is exactly what I was thinking off for thin sheet metal.With those dimensions, I’d likely just buy some 32ga joist lining cut it oversize, and press form it into place or even spray it with something like flex seal.
Go easy early.
My throwout bearing is squealing, and I think I tossed a tooth off the ring gear when i hit the starter.coffee time I finally made it to first gear.
Sheesh leather is expensive
How about using a 1/2 size hot well stainless food pan?The area under the sink is 12.5 inches wide, the water heater is 12.3 inches wide. It is sort of like fitting 10 pounds of you know what in a 5 pound sack. @Coiled suggested corroplast, which comes in 2mm thicknesses or vinyl (like pond liner). These ideas might work. I might also look at getting a thin sheet of metal HVAC ducting and folding a tray up myself.
Oh the joys of custom work…