This is how I install nutserts without the special tool. I'm sorry I didn't get this posted earlier.
Start out with a strip of 12 gauge steel about 12" X 1". Near the end drill a clearance hole of the appropriate size for a bolt that fits the nutsert.
Get a long class 10.9 bolt (same thread size as the nutsert), nut and flat washer.
Thread the nut onto the bolt until it's near the head of the bolt. Slide the flat washer onto the bolt. Now stick the end of the bolt through the hole in the steel strip.
Thread the nutsert onto the end of the bolt until the end of the bolt is flush with the bottom of the nutsert. Slide the steel strip and the flat washer up against the face of the nutsert.
Lubricate the bolt thread that's now exposed between the nut and the flat washer with a molybdenum lubricant (doing it at this point minimizes getting lubricant on the nutsert threads). Thread the nut down until it touches the flatwasher.
Push the nutsert into its hole.
Use two wrenches. One to hold the head of the bolt stationary. One to turn the nut. The steel strip should also be held stationary.
*** This is the key point *** By holding the steel strip and the bolt stationary, there will be no twisting force applied to the nutsert as it is tightened. As the nut is turned, the bolt will be pulled straight out, collapsing and seating the nutsert.
When the nutsert is very tightly seated, loosen the nut a little and then unthread the bolt from the nutsert.
Using this method with the steel strip, you should have no problem with nutserts being loose. I've installed many nutserts this way without any problem (although I still haven't put an X - brace on my car. This summer I hope!)
I hope this helps.