Oh Ps..  My 240z is very flexing.. More and more rubber!   (Just kidding!) 

Actually, I had considered that hole saw idea as a possibility since the metal around that hole is solid. Nice to get some confirmation of that approach. Why not give it a try?

Yeah.. why not..  i was only looking for the name of those rubber thingy's you put in the nice round hole(s)..  

But first i would clean the complete floor as there are often more holes than you think..  My first 280zx had had every 2 years a new layer of undercoating.. when i had it 10 years it was about 20 years old and the technician that checked my car for MOT (Dutch=APK) said to me he could poke right through the bottom at 17 places or so... It had rotted from the inside..  I never needed to put some undercoating on it.. it had a layer of half a cm.. personally i hate undercoating.. grease is best i think, it wipes off and you see more through it when something is wrong.

My latest 280zx has some kind of "silolak"on it.. it's not done by me.. but it's increadable stuff. I ones took of a little bit on the brakeline and after 40 years the original greenish paint nissan used on them came from under it.. in unbelievable good condition.  I wish i knew what the pre owner used.

 

Silolak=silolacquer..

"Silolak" in english can be something like: paint for silo's?  My translator program just says silo for a silo.. it's a big round standing up tank for pig or chickenfood.. a silo..  long ago they were made of steel and they rusted like hell as some foods can attack the steel..  so they had made a paint called silolacquer