Technically you can use the water pan itself to catch your drippings, in the vertical just make sure there is enough water to keep from drying up and time it so your water pan evaporates most of the water out, another words just add a few cups of water every so often towards the end of your cook.
You can even line the water tray with foil, add some water place another layer of foil add some more water the catch your drippings (double boiler), just make sure to leave access to the bottom layer to keep adding water, I have yet to try this but was playing around with the idea.
You can place something like beans under the food to catch the dripping, adding a ton of flavor to the beans, just watch the grease.
Just beware that adding another pan in a vertical will alter the way the food cooks, so rotating the food may be needed.
In an RF, I place the water pan right on top of a cast iron grate that rests on the RF plate, just make sure that it is level because if you have a shallow end, the drippings will burn up on the high side of the pan, just keep topped off with water.
I will save some trimming from the pork and sometimes toss in onions and stuff. For poultry, I dress up the dripping tray pretty good as this will be the gravy.
If you don't want too much smoke just cover the drip tray partially with foil.
Just make sure to remove the fat, before finalizing your finishing sauce.
Hope this helps.