I am pretty sure the gauge was made by AutoMeter. Pretty common company. I will send a picture when I get back from vacation. The tapping in the positive under the dash is a good idea. Just grab one that is on all the time when main switch is on like the radio or lights....sounds like you know this already (but others reading may not).
That is an awesome garage to keep it in. I wish I had one that size so I didnt have to lower it.
If you ever wanted to get under the console where the radio is, open the glove box and remove the screws that hold it together (Phillips) and then remove the front left side cup holder and reach in with a -I think- 10mm long-socket wrench and unbolt. The nut comes off so don't drop it. The nut and bolt is located out of site but it is approximately 3-4" behind where the point of the console meets the hull. It was a little difficult to reach with my forearms and size of cup holder. But once you remove this, there is TONS of wasted room. Hence a battery and amp installed there for me.
I wondered how to get to that extra space under the console. I dont get why they put that stupid little tray on top under the lid. It should have been open space like the other side, thats how it was on my 98. The 15 ft garage door is nice where i store it, but its also 150 bucks a month. Id love to find somewhere cheaper but no luck yet.