I put a fish-tank heater in my 400 litre outside last night, the putside temp was -3, by this morning the water on the tank was +9C.
A couple of hours ago I pumped it round to my van.
What Ive got for tonight is the fish-tank heater now in the van-mount tank and a small 1KW heater in the van to keep poles, pipes free from frost set on lowest setting.
Im determined to go out tomorrow, my main concern now regarding water temp etc is the water freezing in the pipe when its lying on the ground, so hopefully that water in the van by morning will be up to about 20C, hoping this'll be enough to stop it freezing once out in the morning.
Think I'll leave it til about 10am before I go out there though. That'll be okay 5/6 hours.