Do'nt limit yourself by discounting an immersion heater, we have a 3kw one which gives us a full tank in 15 to 20 mins, that will not break the bank. We can also heat water by way of our Ellis gas boiler as well as our caloifier. There is nothing wrong with using some shore power if it makes life easy, we do I might add run a 12 volt fridge and a 12 volt freezer, we use batteries when "out" and charger when "in" It is just a question of getting the balance right.
I agree that many people do put to much reliance on 240v leccy as per a fatboat in our marina that has ahuge range cooker with THREE electric ovens!!!
Phil