magmount

Hello! I have alernator Whine issue on my Kenwood TK-790 Mobile Radio Setup. The Vehicle Everything is in Is a Ford Expedition 2000. I have it configured in a Dualband Setup with a TK-890. Both Radios Controlled with a Single Control Head. The TK-790 Is Radio 2 in the setup and is Connected...

I have a couple mag-mount antennas and really couldn't find anything magnetic for them to attach to. I found an old power supply (turned off) and they seem to magnetically attach to that perfectly! But is this ok? How does everyone else do it? Whats the best way to do it? Piece of steel??