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I have no experience with that particular model, but 2000-3000 watts is quite a draw on just 2 batteries. It might work ok for a quick hand washing, but I would not expect to be able to get gallons of hot water from it.

They do make DC coils for heating water, so you could make a similar setup fairly easily and eliminate the need to go through your inverter.
 

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Assuming 2500 watt usage of 12 volts means that the battery assembly must put out around 200 amps. This is excessive for the two batteries and they will be destroyed quickly. I use an Isotherm or Isotemp 4-gallon tank type heater with a 750 watt, 115 volt element supplied by a 1000 watt inverter.
draw on the battery is 80 amps which is doable from a 230 amp/hour size 8-D AGM battery. I manage the heating by manual switch. Starting with semi-warm water left in the tank it usually only takes around 25 to 30 minutes to satisfy the thermostat. This draws about 40 amp hours out of the battery which has a "usable" capacity of over 100 amp/hours to discharge to 12.2 volts, the recommended level to begin recharge for long battery life.
 

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There are a few ways to heat water that don't draw huge amounts of electricity. They are not cheap or not very elegant. seapro's system uses a smaller amout of electricity and gives you 4 gallons of hot water which for a campervan should be enough and could be turned off when hot which is what he is suggesting I think. The second is to install a fueled hot water heater such as a Wabasto or Espar (Eberspaecher). Wabasto makes them as dual tops which can heat the cabin air and hot water. I think Steve's Backroader has one and he might comment. They are a $2500+ item, burn diesel (or gas?) and are very efficient. Normal 6 gal propane hot water heaters for RVs are relatively cheap ($300) and work fine if you are thinking of installing propane. Portable propane units using 1 lb canisters are also available but are really just for a portable shower.
The third I can think of is a system that circulates the engine's coolant through a coil in an insulated tank. Several manufactorers make such tanks and they might be mounted near the engine but can be plumbed in the van too. <http://isotherm-parts.com/product-range-isotemp-waterheaters-c-4_34.html> These store the heat from when the engine is running.
I have a single 32 sq ft flat plate collector that heats hot water in our AZ house. It provides all our hot water for all but Dec. Jan. and the odd few days it is cloudy there. Very efficient and it feels like free hot water now that it has been in use for 15 years and long since paid for. I have toyed with the idea of a solar panel on the side of the van that could be tilted out and have flexible connectors to a tank mounted above it inside so it thermosyphoned the hot water on sunny days. An 8 sq foot roof mounted panel would give a lot of hot water on a sunny day and a small 12 volt pump could move it down to a tank. Theflat plate may have been done by someone but I haven't seen them. I won't be doing either in the near future.
Lastly there are black tubes and hoses that mount to the roof and collect heat in the sun. They cannot get the high temops of a plate collector behind glass but suffice for off roaders to shower from directly. The solar bag is a variation of this and is a cheap as $10
 

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Whenever I need hot water I just give my wife a hard time and I never run out!
 

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There are a few ways to heat water that don't draw huge amounts of electricity. They are not cheap or not very elegant. seapro's system uses a smaller amout of electricity and gives you 4 gallons of hot water which for a campervan should be enough and could be turned off when hot which is what he is suggesting I think. The second is to install a fueled hot water heater such as a Wabasto or Espar (Eberspaecher). Wabasto makes them as dual tops which can heat the cabin air and hot water. I think Steve's Backroader has one and he might comment. They are a $2500+ item, burn diesel (or gas?) and are very efficient. Normal 6 gal propane hot water heaters for RVs are relatively cheap ($300) and work fine if you are thinking of installing propane. Portable propane units using 1 lb canisters are also available but are really just for a portable shower.
The third I can think of is a system that circulates the engine's coolant through a coil in an insulated tank. Several manufactorers make such tanks and they might be mounted near the engine but can be plumbed in the van too. <http://isotherm-parts.com/product-range-isotemp-waterheaters-c-4_34.html> These store the heat from when the engine is running.
I have a single 32 sq ft flat plate collector that heats hot water in our AZ house. It provides all our hot water for all but Dec. Jan. and the odd few days it is cloudy there. Very efficient and it feels like free hot water now that it has been in use for 15 years and long since paid for. I have toyed with the idea of a solar panel on the side of the van that could be tilted out and have flexible connectors to a tank mounted above it inside so it thermosyphoned the hot water on sunny days. An 8 sq foot roof mounted panel would give a lot of hot water on a sunny day and a small 12 volt pump could move it down to a tank. Theflat plate may have been done by someone but I haven't seen them. I won't be doing either in the near future.
Lastly there are black tubes and hoses that mount to the roof and collect heat in the sun. They cannot get the high temops of a plate collector behind glass but suffice for off roaders to shower from directly. The solar bag is a variation of this and is a cheap as $10
Good summary of possibilities. I'm planning on a 'motoraid' system and I've run the hoses from the engine and purchased a 40 liter Isotherm tank that has a heat exchanger loop. I went for the large tank as it will also act as thermal storage for space heating - about 9kbtu if temp is lowered from 200F to 100F. For normal HW use a smaller tank would work fine and if you need more hot water just start the engine and charge your batteries at the same time. I can't say how well it actually works because it's not hooked up yet. I did post some pics of my hose connections to the engine cooling system.
Bill
 

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The second is to install a fueled hot water heater such as a Wabasto or Espar (Eberspaecher). Wabasto makes them as dual tops which can heat the cabin air and hot water. I think Steve's Backroader has one and he might comment.
My Webasto DualTop (provides cabin heat and hot water) and has worked flawlessly. Certainly are less expensive ways of heating water (my $18 electric kettle does a great job when I only need 2 cups of boiling water for cooking) but I really like the flexibility (heat only, hot water only, or both + automatic freeze protection), efficiency, and comfort the Webasto provides.
 
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