First thing would be to drain the tanks on both truck and trailer. Get all the water out of them. And it'll take a few times so don't think once will get the job done. Open em up 2 or 3 or 5 times throughout the day.
Air line dryer might get you through the day. But what about tomorrow.
Once I got my tanks drained. I would drain em every day during the day when the temp was warm enough. Waiting till parked was usually too cold to drain em.
Working for a company that isn't too cheap to replace the cartridges in the dryer helps out also. Water in the lines usually isn't a problem with fresh cartridges.
It doesn't need 2 tanks to have a regulator. My trailer only has 1 tank and has a line coming off the tank to a regulator the to the leveling valve. My last trailer same way and when the regulator took a #### I just took it out and plump straight through. Probably not the best Idea.
Sounds like you need a new valve. Should be 2 valve on it, 1 for the maxi's and not that much money and 1 for brakes and probably ABS and is pricey.
I had the opposite happen on last trailer. If it was below 30 I could drive away without pushing the red button in and charging the trailer. I could be going down the road and pull the button and nothing, but brakes work and suspension air up (as long as button was in). As soon as it was 33 out it worked. Changing the valve fixed it.