I have a trunk mounted battery in a Chevy Nova. The battery is not in a plastic battery box. I run a one wire alternator that charges 14.6 volts max. After about a month, everything metal with the slightest scratch within two feet of the battery develops corrosion. The terminals generally look good. I have tried three different Bosch batteries with the same result. The batteries are standard 12 volt and are sealed---at least no place to add water. I have mounted batteries in the trunk of other cars before without an issue. What am I doing wrong?

Sounds like battery is out gassing badly I would try a battery box. Where is battery grounded?

If the battery is gassing, there is a problem, always.
Overcharging, undercharged, shorted cell....

Is the compartment vented at all?

Are you using a maintenance charger in between races?
You could be cycling the batteries too deep.