Thank you all again for the useful advice, and I will keep in mind that canals do have shallow ends.
Our intention is to live aboard for a couple of years, our major concern at the moment is our ability to cope with life in a corridor. Two weeks in winter where the great outdoors is not so hospitable and available for relief seems a good way to test this. We both are used to cold weather, I've lived a long time in Switzerland, and my new better half is from New England (it snowed over there yesterday) so are used to cold winters and have the gear. It is the cold damp grey English winter I remember from my youth that worries me more rather than the colder clear blue sky winter days we're used to. But as has been said, solid water may cause some problems in a really cold spell.
From what I gathered reading all the words of wisdom on this site, I suspect that it is unlikely a hire boat will have the battery capacity to last even a couple of days without extended use of the engine. My thoughts are to have a word with the hire company to see if they would allow us to moor up and hook up at their base should we be unlucky and hit really bad weather during our test weeks. Thanks for the reminder that hooked up to mains on a mooring is a viable winter alternative.
Thank you all again for your advice and tips, and the words of encouragement and the warnings. We want the sense of adventure of living on a narrowboat - reading extensively on this site has not put us off, with descriptions of the many ways of sinking the boat, narrowboat neighbours from hell, and malfunctioning equipment notwithstanding. We will also use our test time on the canals to look at a few boats for sale to get an idea of what you get for the money, and how the various boat layouts look in real life. We have budgeted around £40k for the boat with another 5k reserve if needed to add the extra creature comforts (preferable not as a recent divorce severely dented the bank balance). I'm thinking we should be able to get a boat well suited as a liveaboard in good condition for that money. I will no doubt come back on here for detailed advice on the finer details of equipment and boat purchasing if need be, although I am impressed at the amazing amount of information already on this forum.
huymog