A decent inverter will cost about $375 to $550 (northerntool.com),thats in the 2500 to 3000 watt range and is most likely twin 110 volt outlets. Hope your water pump is'nt 230 volt,but I'm sure if you do a search on the net a 230 volt can be found ! All in all , it may be a stretch of the concept to allow our trucks to idle for a long period of time with so little load . Especially in winter. I've got a generator (5000 watt) gas aircool,and find that on a short outage(wich happen often) I wuold rather use a inverter in a truck for a couple of hours to run things like microwave,tv,fridge and lighting mainly in the evening before bed. On long outages I have found the gas aircooled gen. is the only way to go as I have a transfer station wich allows whole house except air conditioning(I'm on well water also),but never leave gen. running while off-site. The air cool gasser is mildly annoying hollering away at 3600 rpm too !Although the entire set-up priced out at $500 Gen + 250 Trans station + 100 misc wire & fittings + 100 fuel and cans (in storage w/ treatment to extend life and I still rotate it every 6 months) So there is what my spin on it is , Hope this helps and as you can see there is no easy answer whithout the short term long term Vs. load /frequency of outages equation !
Mark T.