I am not sure about the 800 watts for the charger. but there are several possibilities. "The Travel 801’s input power is 800 watts. Rated power is 29.6 volts. Final charge is 33.6 volts." (from the brochure) So, you should be able to rig up solar cells in series to provide a charging circuit. (three 12 volt solar panels with a 36 volt regulator)
Next, the inverter/charger: If you need 800 watts for 12 hours, this is a lot of power! and I question the amount, based on the following: 800 watts at 12 volts is about 67 amps--take into account ineffeciency of the inverter you are close to 70 amps for 12 hours--or a total of 840 amps. (I could have just used the 800 watts/direct conversion for 800 amps)--so if you have a 550 amp hour battery bank--which the Dreamer bank is--you would have run it down over three times (figuring 50% discharge max--or 275 amps effective available power). An outboard alternator puts out 35 to 45 amps (average) when running at full power, but that is only half of the 70 amps you will need. So this does not seem like a real effecient way of charging these motor's batteries--assuming it really needs 800 watts! So basically if it needs 800 watts for 12 hours it requires about 3x the two 8D battery banks....that is why I doubt the current draw.
Consider that the capacity of the battery is 800 watts @ 30 volts or 26 amps--that is perhaps more reasonable for a lithium ion battery. (the equivilant to about a 70 amp 12 volt battery--which is like a U1 or garden tractor)--and I suspect this is closer to the power. If this is the case, the power for a charger is signivicantly less. Some one with one of these chargers has to measure how much power it uses, or write the company.
I suspect that the charger will be more in the way of several amps at 110 volts or 10 to 20 amps for an inverter--and this is managable.
Yes, EU 1000 will produce 900 watts, but that would be running at full throttle, not eco throttle.
I would have to assume that the best use would be to leave with a fully charged battery (and perhaps a spare) and then recharge when you overnight at a dock (or use the solar cells).