Batboard

I have been asked to reinstall an antenna on a CV (former Calif. Hwy. Patrol). The holes have been patched with a bondo type material. Can these holes be opened up easily? I recall trying to do this some years ago and the bondo cracked and chipped easily. The base of the new antenna barely covered the cracked material. My alternative is to just make a new hole in the metal. Any info would be appreciated.
Thanks
Ken

One thing you must be careful of: The hole might be larger then a standard NMO mount. You might also crack the bondo and it wont look good at all... You might be better off just starting with a clean hole - THen you know for sure it's the right size.

the bondo will not make for a good ground is it is bigger than the standard hole or crack under the pressure of the whip boucing while driving