Is this a new TT? The standard is....White wire is GROUND (should go to the frame), BLACK is POSITIVE. The RED, I would think it may be the main 12VDC source for the TT, but I would recommend tracing it out first, just to be sure.
Only AGM batteries and (LiFePO4 $$$$$$$$$$$) can be SAFELY installed inside the TT without venting, flooded batteries have to be in a sealed box and vented (to the outside) box.
Check out our
RVing with SOLAR social group here on the forum. A lot of good reading here.
My Registry
Don