I picked up a Masterbuilt Dual Fuel propane 2 door smoker at the beginning of July and after the first few smokes running apple wood chunks in a cast iron pan, I decided to try out a AMNPS pellet tray. The goal was to try and get a longer duration of "unattended" time where I wouldn't have to reload wood chunks since they only last for anywhere from 1 to 1.5 hours.
After some research, I learned that it isn't recommended to run the AMNPS tray inside the Masterbuilt cook chamber, so I went the "mailbox mod" route which keeps the AMNPS pellet tray in a secondary container and pipes the wood smoke into the cook chamber. Most guys on here use an actual mailbox, but I had a old charcoal grill (Smokey Joe knockoff) that I decided to repurpose for this mod. With some parts from Home Depot, ducting was run from the mini charcoal grill to the Masterbuilt smoker without issue.
Looks good right? Not quite...it turns out that smoke from the AMNPS tray gets sucked down into the propane burner when it's turned on, instead of flowing up through the cooking racks. This means you might see a whiff of "thin blue smoke" out of the top exhaust, but it's maybe 10% of the smoke that's getting piped in from the AMNPS tray. I smoked a Boston butt with this setup and the meat hardly picked up any smoke flavor.
The next challenge... how do I prevent the propane burner from sucking the wood smoke downward? I tried a bunch of things along the way, and to save you the details I'm currently using a inverted veggie grill basket (full stainless steel piece from Weber) over the propane burner, and a hacked up stainless steel baking skeet sitting on top of the veggie basket acting as a baffle. I'd say 90% of the burner is now blocked off from the cook chamber. I thought that was going to do the trick, so I fired up the AMNPS again to test. Somehow, the smoke still manages to get sucked down or dissipates with this setup, so I start thinking that maybe I need to install another exhaust at the top of the cook chamber to create a stronger draw of air that will suck the smoke up. With this in mind, a 3.5" hole was cut in the top of the box and unfortunately things didn't get better.
I thought maybe I needed a smoke stack...so I threw a extra piece of A/C ducting reducer I had from when I plumbed the charcoal grill "mailbox mod" into the smoker. The reducer was about 8 inches tall...and that did nothing. I thought maybe a taller smoke stack was needed, so I purchased a 2ft long stove pipe. Things seemed to get a little better, but the smoke coming out of the smoker was really thin. Being beyond frustrated at this point, I decided to light the AMNPS tray from both ends for maximum smoke output. Things looked a little better, so I ordered another AMNPS tray from Todd so that I could burn 2 of them at the same time. The charcoal grill needed to be modded a bit to fit 2 AMNPS trays, but that wasn't a huge issue.
Even though I don't have the 2nd AMNPS tray yet, I decided to test things out yesterday by doing a "quick" smoke with some spare ribs. The AMNPS tray was lit from both ends, spare ribs were cooked at 225F using a 3-2-1 method. The result? Ribs that were hardly smokey... I had "TBS" pouring out of the smoker the whole time, I have no idea why the food isn't getting good smoke flavor! In addition to the ribs, I also threw on a batch of ABTs and those didn't really pick up a smokey flavor either.
I'm now at a loss of where to go from here. I have a few hundred bucks in modifications poured into this smoker (with a 2nd AMNPS tray and 20lbs of pellets incoming from Todd, to join 20lbs I already have), and it seems like trying to get a pellet tray to work with this propane smoker for hot smoke is a huge bust. I'm pretty much out of ideas at this point on other things I could try to do to remedy the problem.