The snow helpfully held off until about 11am, allowing me to get another 2 car loads of horse muck into the hotbed. That was enough to fill it full enough when trampled down. I now need to add some of the used compost from last year's plants and find a large piece of bubble wrap to cover it with, and leave it to heat up.
There was just time for a couple of photos before snow stopped play:

There was just time for a couple of photos before snow stopped play:
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