This sounds WAY too familiar...
I was an electronics professor... hope I can help!
Your trailer sounds exactly the same as my configuration. Here are the schematics for the interior 12V
DC system of the 1971 27-31' International. I have recently redone all of the electrical in my trailer. Assuming the electrical system didn't change completely in 1 year, your blue and white wires are your charge lines, 12V
DC and ground respectively which run from your tow connector to your univolt (primarily). From your univolt (which should be in your passenger closet), the charge lines break into various circuits that distribute power to your 12V
DC appliances; these circuits should be fused and color coded. In other words, different sections of your trailer should have like colored +12V DC wires connecting to the various appliances e.g. my kitchen is purple, bathroom is yellow etc... Those should be your 2 phantom red wires. You can check by using a multimeter to measure the voltage across each line to test:
V_blue > V_white = 12V
V_red1 >V_white = 12V
V_red2 >V_white = 12V
In my case, I found red wires connecting to the vanity lights that were not labeled on the schematic at all... You'll just need to test them with respect to ground to see what you get, and then decide what to do with them e.g. terminate, add appliance etc...
There is also the strong possibility that there used to be a switch between the 2 red wires, which would mean one red line could be +12V and the other would be 0V, or they could both be 0V and been powered via the blue line. If you find another dead end red line or an appliance with a red connection close by then there was probably a switch there to provide power down the line.