Stripped AC suitcase mounting holes
 

I went to install the AC suitcase an noticed about three of the firewall mounting holes were stripped or marginal.

I went ahead and drilled them all out and installed 1/4 - 20 rivet nuts and ordered some appropriate length black oxide flanged bolts. The rivet nuts do have a flange that is a bit proud of the firewall, about .030", so I added a bit more butyl on the case to seal. Going to use some never seize on the bolts which should prevent the them for seizing and twisting the rivet nuts in the distant future.

Anyone else come across this? Think this solution is appropriate?