Back strap in the smoker
 

How long will it take to smoke one in a gas smoker... My tekp can go from around 200 to 400 degrees...

I'm thinking 250-300 degrees for about a hour or so...

Smoke to temp, not by time. I'd do 225-250 till you get an internal of about 135* wrap in foil and let rest about 20-30 min before slicing.

I did one yesterday in my GOSM...averaged 225 degrees and it took 1.5 hours to reach internal of 140. Absolutely delicious.

I did some a few weeks ago. I kept the smoke at about 225 degrees. I did loins and back straps at the same time. The loins were done in about half hour. The back straps took about 1.5. i just cut mine in half and did not butterfly them. You might butterfly them and get them done quicker. Also if you can keep a thermometer in the meat ( a remote sensor,or a long one that will reach through the top vent) it will keep you from having to remove the lid several times to check temps. I've heard that temp times increase by ten minutes every time you take the lid off.