Have you also considered the tri-fuel kit for the Honda EU2000i. You could go for about 10 days when connected to an industrial 47kg Propane bottle.

http://www.generatorsales.com/honda-generators.asp

http://www.generatorsales.com/order/Honda-EU2000i-Tri-Fuel-Kit.asp?page=Honda_EU2000i_Tri_Fuel_Kit

Storing propane is on site would also probably be safer, more convenient and won't degrade (i.e. you wouldn't have rotate the fuel) unlike the quantities of petrol required for the same power duration. Plus it would also reduce the constant trips to the generator to refuel the tank.