Snakes and Turtles as Tank Mates

I have a red eared slider that lives in a mostly aquatic terrarium. He has landing areas and I plan on making improvements to make the tank more natural (i.e. adding soil and plants on one side making a divider so that the other side can be strictly water). Recently I found a baby Black Rat Snake and was wondering if I could keep him in the same tank since I don't have the funds to set up a totally separate one. Could these two be tank mates? The RES is about 6 or 7 inches long and the snake still has his baby markings.

Mixing species is almost never a good idea. It will just stress both of the animals out by constantly being in the presence of each other. Red-eared sliders are also omnivorous, so there's a chance it may eat the snake or snap at it and injure/kill it.
   
Also, a large adult RES needs a 125+ gallon tank. An adult rat snake needs a 30 gallon tank. To house both comfortably and to minimize the contact they would have with each other, you'd need a tank in the 200+ gallon range.
   
I'd also imagine a turtle tank would get quite humid, and I believe high humidity causes mouth rot in some species of snakes.
   
I just personally wouldn't do it. :p

thanks so much for the advice! i ended up giving the snake to a friend. i thought about it and realized my husband would probably kill me if i brought home another animal lol.