I have a 22 inch weber BBQ.
Weber 22 inch Premium Grill
It smokes pork loins really well. You need these
Charcoal basket
Chimney starter
Aluminum drip pans
And you need some small untreated wood blocks, apple or cherry are the best but hickory works as well
1. If wood is very dry, soak in warm water for about one hour.
2. On one side of the grill place one of the charcoal baskets under the folding part of the grate.
3. Open the bottom of the grill all the way.
4. Start briquets in the chimney, about thirty of them. I usually put newspaper under them, pour a little vegetable oil on the paper and put briquets on top and light the paper.
5. When brickets are mostly grey, fold back the grate and pour them into the basket.
6. Place 3 to 4 pieces of wood on top of briquets.
If you bought a whole loin, cut it in half. Give it a rub or how ever you would like to prep it. I use fresh garlic, and pepper. If you have 24 hours, rub it with fresh smashed garlic, pepper and salt, wrap it tight and store it in the fridge. If you do not have 24 hours, just garlic and pepper. Place it in the foil pan and put it on the prepped bbq opposite the fire. Put the bbq lid on (the lid on this one has a thermometer). Open the vent on the lid all the way for about five minutes to get the heat raised up. Partially close (1/2 to 2/3 of the way) the vent in the lid to slow down the fire and keep smoke inside the bbq. Temperature should climb to about 300 degrees.
At this point you can run it for an hour or so. Watch to make sure smoke is seeping out, replenish charcoal and wood as required. The idea though is to leave the top on most of the time. After an hour take the temp of the loin with an instant read thermometer. It will not be done yet but you could remove it and finish it in an oven if you only want light smoke flavor. Either way, cook the loin until the center reaches 160 degrees. At that point, remove from heat and let rest, lightly covered for 1/2 hour. Serve 1/4 to 1/2 inch slices with corn on the cob and what ever other stuff goes with a bbq.