Hi David
I insulate my boiler with hot water cylinder cover stuff like this:
http://cgi.ebay.co.uk/NEW-HOT-WATER-CYL ... dZViewItem
I got mine for about £8 from ebay including postage if I recall rightly, so don't pay silly money for it.
Here's an old picture. I connected it to the boiler with that elastic stuff you use to connect stuff to a roof rack, if you know what I mean (from a pound shop).
The benefit of this stuff is that it is plastic, so any spillages can be wiped off; on the other hand, if you use an old sleaping bag you don't have to pay anything.