Retrofiting a Drip Pan in Wet/Dry

It should be fairly simple. Basically, a drip tray consists of a sheet of acrylic roughly the same size as the bioball chamber, with a lot of holes drilled in it. 1/8th inch holes are probably about right. You will also want to glue a shallow lip around the edge of the drip tray, maybe 3/4 of an inch or so, so that the water actually exits through the holes instead of mostly running off the sides. Finally, you will need some kind of lip attached within the bioball chamber to rest the drip tray on. Leave the drip tray loose, not permanently attached, so you can remove it if you ever need to. Then simply pull the spray bar off and let the water dump directly onto the tray. That should about do it.

Is your wet dry a converted fish aquarium or factory made filter?
If it's an aquarium I can show you some photos of what I just did to mine for a nice drip pan solution.

I made the drip plate so it would rest on the lip of the aquarium, then I built up a box with thick lexan and sealed the box with silicone. I'm still working on a permanent lid for it.

When I need to remove the drip plate, it just lifts right off.