On Dec 11, 2013, at 10:28 AM, Steven Johnson <sjohnso2000@GMAIL.COM> wrote:

 It uses otherwise wasted heat and
has fairly
minimal impact on space (YMMV)....   I'm not traveling like I used to but
I'm still
considering putting a similar setup in mine.    I'd like to "sort-of" have
the hot water
stored in maybe separate containers in the engine compartment toward the
side
walls away from the engine itself so as to keep the underseat area free for
other
storage though.   Haven't found suitable containers yet.    I'm open to
suggestions.

Insulated storage water tank under the van, using the coolant lines near the radiator,
plumbed over to the spare tire well where you install a "heater" tank with the copper coil
in it and a pump so that once the water is heated, it is pumped to the insulated tank.
Example exterior tank: http://www.eurocampers.com/Vanagon-45L-Grey-or-Fresh-Water-Tank_p_443.html
This one is made of very robust/thick plastic and because of the large opening, it may even
be a candidate to install the coolant-to-hot water storage coil right inside of it rather than
a remote heating tank up under the spare tire well.

Going to the expense of storing the spare tire on the rear of the van opens up a huge
space in that spare tire well. I put a Viair compressor and a storage tank in there and 
there is still a lot of space for "other".

Bob