Lou,

You're sure right about needing metal under a mag mount.  I lived in San Francisco for several years and used a 5/8 wave on 2 meters for most of that time.

I did have it on a big iron skillet and it actually worked very well.  

I was even able to do quite a bit of work on simplex in the SF bay area with the thing and could even work distant repeaters.  

Actually, in San Francisco, it was almost better than an outdoor vertical because that place has to be the capital for intermods.  You'd have to hear it to believe 
it.

Anyway, since I'm really looking for an antenna just to get going around here, a mag mount sounds like a fine way to go over the short run.

Don