This is offered as an FYI from a complete newb so take it for what it's worth.
I had a very difficult time getting temperatures up this weekend. Took 10 hours to smoke some summer sausage, then Super Bowl Sunday I spent all day and BARELY got my ribs and chicken done. I've thrown out the chicken because I feared I may have stayed in the danger zone way too long. I lost track of time but guessing after 4-5 hours finally JUST hit 165°. The ribs were done but never pulled back and definitely not "fall off the bone" tender.
I thought my thermostat control was failing as I had to crank the temperature up, and up, and UP all the way to the top setting (275° I believe) to get my IT to 165, and the compartment temperature would barely climb above 200°.
But I had covered all the bottom stuff with foil to catch drips and help with clean up. I just laid it in the bottom (actually over the top of the upper drip pan that covers the chip tray and drains to the water pan), leaving about an inch of clearance in front and back. I believe I used too big of a piece and it just deflected and reflected the heat back downward.
Monday I removed the foil and ran it dry and it heated and held temps at the settings.
So bottom line, I've decided the clean up isn't so bad, and I'll do away with the foil altogether.
IF you opt to use foil in the bottom I'd advise to JUST cover that drip pan over the burner and chip tray. Otherwise, you may have difficulty getting the heat where it needs to go. And before I did this, I would maybe do a dry run with and without the foil and compare.