You would never want to use a whole tray of wood chunks in these smokers unless you wanted everything to taste like the bottom of an ashtray. In fact, if you do not already have one, I would strongly recommend buying a digital scale that measures in ounces.
These smokers really do not need that much wood and will smoke for quite a long time. Smoke only absorbs until you hit about 140 degrees. So, any smoke applied after that will just rest on the top and make the results bitter.
You will want to measure your wood in ounces, not how many times you have to fill up the wood box. And to be clear, you only add wood at the beginning of the smoke and do not need to continue to add wood. The most wood you will ever want to use would maybe be a butt or a brisket at 5-6 ounces (maybe 7 on a brisket). For shorter smokes like small roasts, steaks, and ribs you would be looking at 3-4 ounces and for poultry 2-3 ounces.
The following thread includes a pdf doc with recommended times, temp and wood:
Guide to Smoking Times, Temperatures and Woods
Since it sounds like you might be new to this type of smoker, I will give you a little heads-up that many of the processes that you have had to use with traditional charcoal, wood, or propane smokers are simply not necessary in the Smokin-It smokers. For example, you can/should skip the foiling (ie 3-2-1, 2-2-1, etc), texas crutches, mops, and spritzing. Foil should only be needed to line the bottom of your smoker and the smoke box.
Hopefully, this helps. Please let us know if you have any further questions.
I almost forgot welcome you to the Smokin-It forums from ND and to suggest that you start a thread in the Introductions section (if you haven't already) to tell us a little bit about yourself and what you like to smoke. You will also see that most of us put our name and location in our signatures. We are a family here and like to know our new friend's names and where they live.