That should be a good battery for the job. When I first see acid spillage it's usually because overcharging or overheating is boiling the battery acid. In the trunk it will not be overheating.

When I looked up your battery the pictures I saw made it appear to be sealed (no removable top caps) and vented with the GM style oval vents.

If it were me. I would do the following.

1. Hook up a Voltage meter and check for voltage going over 15v while driving and racing if that is your application. Bench testers do not spin an alternator as fast as driving/racing it will.
2. Hook up an ammeter and check the flow of current. It should be near to nothing once the battery is recharged after starting.
3. Hook a vent tube to the vents and place that tube into a jar to see if the acid is coming out of the vent tubes or possibly a crack in the battery.

Definitely a little puzzling because you seem to have done everything correct.