I've got a GOSM propane fired smoker, and one of the common complaints about this unit is the rather small size of the smokebox, which means that you'll need to replenish it sometime during your smoke. I've tried using 8x8 and a 9x13 cake pan and wrapping it in aluminum foil, but was still having problems with flareup. I remembered a covered aluminum cake pan that my mother had long ago. The cake pan had a rolled edge,and the aluminum cover used the edge as rails and slid securely over the top of the pan. Well, those pans are collector's items now pretty much, but I did manage to find the successor to those pans.
Ace Hardware sells a Mirro 9x13 cake pan that has an aluminum lid that snaps shut over the top of the pan. You have to buy a box of four of them off of their website, but it fit the bill perfectly! I drilled six small holes in the cover, and used it to smoke a turkey today for Christmas. It worked flawlessly. Even though you have to buy four pans and covers, I'm sure you'll have no problem finding family members who would like one. My mother has asked me for one of mine.