Hi All,
Just thought I'd share this with you - any suggestions / comments how this could be used better

Have recently purchased a submersible low volt hot water heating element, (similar to that used by farmers to stop their animals water troughs freezing over), though this you can plug into the cigarette lighter of the van.
I've screwed it to a standard 25 litre barrell cap and I set it in a full barrell of water, before I set off to a job.
It takes approx 25 minutes to warm the water up to a decent temperature (not ideal for everyone), I then use this to fill up my backpack - hey presto - a hot / well pretty warm water backpack !
I then swap it over to another full barrell as I drive around and heat this up as I drive. Seems to work pretty well presently. Though still a bit concerned that a leaky barrell may cause me to electrocute myself as I drive

Had a flat battery yesterday though

. May have to sort a second battery for it
Cheers, Dave.