I see nothing wrong with using a divider, I was asking because there's risks housing snakes together and wanted to see if that's what you wanted to do.
Have you looked into a room heater on a thermostat to keep ambient temps up? I think if you have a room designated for snakes then a space heater may be the way to go, especially if you may want to use a rack/tubs again. May be easier than heating your entire house to a ~80-84 degrees to keep the ambient temps in the tubs up to where they need to be.
I'd also look into radiant heat panels for the cage to bring ambient temps up, though I'm not sure how that would work in one cage that's divided in two (since usually the RHP is used on one side -that I'm aware of- since the snake still needs a hot and cold side).