If the insert is spinning in the tank, just pull out the insert with a tug. Then go to the hardware store and get a metric nut that fits the shroud bolts. Get some 2 part epoxy. Clean the tank VERY well, then epoxy the nut into the hole that the insert was in. Let dry for 24 hours. If the tank was good and clean, that nut will stay there forever. Take a look at the bikes I own, I have had those problems too. Make sure not to overtighten the bolts and DONT crossthread them, or you will have those problems.
Dave