1. The fact that you have a [b]UHaul can point to significant clues if you know the differences between your trailer and others.
2. [b]How is your trailer different?
[b]UHaul Trailers were designed and built to be short term rentals
for regular people. They had to be designed to survive treatment from people who did not tow a travel trailer very often. Therefore, they had to operate pretty much on their own with minimal training.
"there are two red wires run under the frame (one's grounded) and the up inside near the battery. Are these intended to charge my deep cycle batteries while driving?"
I am assuming that these are extra wires, and not the wires that power up the "house" lights and water pump (if you have one). You assumed that they were supposed to connect to your tow vehicle.
But they cannot with only a 4-pin flat connector. If they "Come up near the battery" and "one's grounded", where does the other one go to? That is the $64,000.00 question. I would suggest you look on the roof.
Why the roof? Because [b]UHaul installed a 12volt evaporative cooler and a solar panel
up there. It would be the [b]solar panel
, and not a charge line from the tow vehicle, that would keep the house battery charged up. No fuss no muss for the customer renting the trailer. Minimal down time for [b]UHaul.