Masterbuilt owner here so take everything I say with a grain of salt.
I think all pellet cooker vendors shoot for 4 things:
1. uniform temperature across the grill surface. People complain when the burgers cook at different speeds. I have low expectations here and consider moving meat around just part of cooking. YMMV
2. Ability to reach high temperatures (basically sear a steak) which basically conflicts with #1 above. Again not a big deal for me...I either use the pellet crucible to start a basket of coals and charcoal grill in the pellet machine (for 1-2 steaks) or separately start up my
Weber kettle (for >2)
3. Ability to slide grease/oil to the outside world (bucket or tray) where it's not a flare-up hazard. (Not a big scary thing to me...I cook far from wood structures and always have a hose handy even if I misjudged things.)
4. (This goes hand-in-hand with Number 3) Making clean-up easy for the owner, even after a large amount of messy chicken, etc. (I figure I've never had a clean grill before, why start now?)
Since none of these are that important to me, and I love to tinker, I seldom use any of the stuff that comes with pellet machines and play around instead with cast iron pans on 3/8 rebar stands, etc etc. You're proposing a baking pan, which isn't unlike my CI pan (which I put pellets in because I want more smoke flavor) but I think you'll want whatever pan you have over the crucible to have a very think bottom (like CI) to help spread the heat out. Also I'd avoid aluminum directly over the crucible...it gets incredibly hot!
And if the 4 "market-driven" reasons above are important to you, I wouldn't recommend tinkering around at all like I do.
You didn't ask but I've also added a water pan with heater element (because I like to adjust cooking humidity) and I've also added manual control to the induction fan speed...which isn't without safety ramifications that I'm relying on staying alert about. If you think this all sounds crazy, well you've been warned.