roadtrek zion srt

We just took our first long trip in our 2018 Roadtrek Zion SRT and are experiencing a new issue. We have the batteries on and the inverter off to power the fridge and keep our food cold. After a few hours of highway driving the voltage meter goes dark and it stops powering the 12V appliances...

Does anyone know what brand TV antenna came with the 2019 Zion SRT build? I looked on the make/model spec sheet and it only says TV Antenna. Google search only came up with the typical "this Zion SRT is for sale" algorithm. I searched the posts here, but didn't find anything. The reason is I'm...