If you're intent on cubing upfront, you might consider a 20" pizza screen. They're like $4 at a restaurant supply store, $10 at Amazon:
https://www.amazon.com/exec/obidos/ASIN/B001CICFBQ/tvwb-20
I also think you could get away with a disposable foil pan with open top. You could poke some holes in the bottom for drainage, if you're concerned about that. They'll get plenty of smoke on the exposed surface from above, and you can always stir a few times for even exposure.
Curious to know which recipe you're leaning towards trying.
This is the one I'm going to try. You smoke 3 lbs of pork belly whole, then cube it and finish it in a disposable foil pan. Should be adaptable to the WSM and to your 9 lb belly:
https://www.texasmonthly.com/bbq/smoked-in-texas-bacon-burnt-ends-at-heim-bbq/
This recipe from WSM guru Harry Soo slices the 3 lbs of belly into strips and smokes them, then cubes at the end to serve:
http://www.slapyodaddybbq.com/2017/06/pork-belly-pig-candy/