you could simply buy the dc chargers for each. there is (guess they still do it) have a dc outlet by the tv. why waste the energy up converting to ac then down converting to dc? the computer, u may have to. my laptop power supply is capable of ~80 watts out (19 V and 4.3 A). i have a 17" screen. the one from a few yrs ago required much more (abt 2X+) and a 15" screen
carrying water, i'll give u a left field answer that actually happened to me. i always ran dry or near dry. one day i pulled into a full hook up rv park in Nebraska (there were aliens on the water tower...should have tipped me off) and they lost the water well abt an hr later. i carry abt 10 or so gal of water now. i use it more to flush the toilet while on the road.
the weight consideration, if ur close to a limit, is a valid one. don't ever believe u will see it on ur gas millage.
as already stated, watts=volts X amps. that balance will exist on each side of the inverter. you will also get a small loss that will be consumed by the inverter.