I made my first smoked meatloaf tonight, and I have to say it is fantastic!! Here's what I did:
2 lbs 80/20 beef
1 lb pork
1 packet meatloaf seasoning
1 cup bread crumbs
8oz (half jar) of medium hot salsa
1 egg
So a really basic meatloaf recipe -- I used salsa instead of chopping onions and peppers to save time, and because I read it on some recipe online.
I then took a sheet of parchment paper and put it on top of a cutting board and formed three 1lb meatloafs. I figure more surface area equals more smokiness to enter the meat.
Cheap vertical smoker at about 225, I transferred the paper and meatloafs onto the grill grate.
Used about 1/3 apple and 2/3 hickory to smoke... smoked for the first hour.
Inserted wireless probe to go off at 145 degrees.
Back inside, mixed up
2/3 c ketchup
4 T brown sugar
2 T white vinegar
If I had apple vinegar, I would have used that instead. Anyway, put that in a saucepan, heat until everything is combined nicely then turn off and wait for the temp of the meat to hit 145.
Once the beeper went off, I went out and sauced up the loafs, then set the beeper for 162. I also threw in some more coals to put the temp more towards 275. No chips at this stage, just cooking it off.
Rested five minutes, then tore into one of them. Unbelievably good -- <Fieri>nice smokiness in the meat which contrasts with the sweetness of the glaze.</Fieri> Highly recommend.

As an edit, one nice thing about smoking this on a vertical smoker is that the fat can run off the parchment paper and it doesn't stick around the bottom of your loaf. I would probably rather have meatloaf on the grill w/o smoke vs. meatloaf in the oven for this fact alone.