I use to keep newts for the exact same reason, I had good luck keeping them in the basement (was the same temperature all year). What are your plans for substrate? I had smooth gravel and river stones in mine because I had tried to mimic a stream in a 20L. If I find any old pictures I'll definitely share them.
Would love to see pictures!
My plan for substrate is aquasoil base with sand on top with a few pieces of gravel mixed in for aesthetics. I don't think I am trying to do a carpet in this tank but I find it useful to add a few handfuls of aquasoil into the bottom of a tank.