Have you thought about putting a second heater in your DT, maybe the over flow if you have to but i think in the main DT would be best with this setup. Maybe get a bigger heater for your sump and set it a little higher, I would get some kind of controller for your heaters though, cause they will break one day and that always sucks.
I have a 200gal salt water storage tank in my back yard with a 300 watt heater in it and it can barley keep up at night and our night rarely get below 50f, Also as you stated the tubing below your house is killing the heat from your sump. I have my tank connected below my house as well and when i do water changes the first 5gal or so are freezing then you feel the temp jump once you get the water that was in the tank.
I have a 200gal salt water storage tank in my back yard with a 300 watt heater in it and it can barley keep up at night and our night rarely get below 50f, Also as you stated the tubing below your house is killing the heat from your sump. I have my tank connected below my house as well and when i do water changes the first 5gal or so are freezing then you feel the temp jump once you get the water that was in the tank.
