As for heating, I use a 'heat-cabinet' that holds my two water barrels.
I've since lined the inside with rigid Styrofoam for better heat retention.
I use a small 'parlor-heater' to keep the interior near 100 degrees
in freezing weather. This has worked at temps 12 degrees below zero.
These are the pumps I use and have used for years.
They are magnetic driven with no oil to escape into your water system.
They are safe and Pondmaster makes them. I run them 24/7, 365 days a year.
Contrary to what you will hear, I've never had issues with 'algae' of any kind.
I like the fact that the water is circulating in the pipes at all times.
These pumps are meant to run continually for years at a time.
I "DO" keep a spare on hand......just in case.
http://www.relaxingdecor.com/Pondmaster ... _1244.html
I'm sorry to say, those 'heat-wires' are a pain to use and you cannot make
any additions, nor reductions, to your rabbitry once they are in place.
If it freezes due to power failure, you may as well trash them.
It's nearly,
"if not" impossible to make any repairs to your system when you use them.