I have to agree with JMIII, I have put several plugs in my truck tires (F150 and a Ranger) with no problems at all. I had 3 plugs in the same tire on my Ranger, one went in when the tire had less than 200 miles on it, it went on to live a happy long life. They hold air fine, easy to install, and a darn sight cheaper than a new tire. There are a few exceptions. I wouldn't put one in a performance speed rated tire. And NEVER put one in a motorcycle tire. Balance is way to important, and in the unlikely event that the plug should let go, the results are much more catastrophic. In an unloaded tractor tire, I see no problem at all with a plug and wouldn't hesitate to do it myself.
Farmer kid usetabe, Farmer Wannabe