I wrote the article on this procedure. Several Viper owners here in Denver have done the fix with no problems. It sounds as though you are not squeezing the tool hard enough to fully clench the rivet. It takes both hands, with lots of grip power, and you cannot damage the tool. Get someone to help you if you don't have the grip required. Also make sure that you have drilled the correct hole size. If you drilled it too large, it may not work. For the 10-32 cad. plated steel rivet nut, the hole size should be 19/64 in. diameter. Also, if you made a ratty hole with a dull drill, it may not clench properly. If you are not experienced in this type of mechanical work, get some help from someone who has done it before. I hope that you are not using the aluminum rivet nuts that came in the Marson kit; they are too soft. If done correctly, with the cad. plated steel rivet nuts that I recommended, it works very well, and it's not that difficult.
I have had my sills off many times since the installation and have had no problems.
Call me if you need further help.
Jerry Scott
303-697-0662