some interstate rest areas in CO have fresh water fills (the ones with dump stations)
but WHY hold off till close to the campsite?
just fill the tank at home and TRY it.
hauling water will have very little impact on mpg
and a full fresh tank is considered a GOOD thing on a stream,
many believe a FULL fresh tank will improve towing/stability by lowering the center of gravity.
your tv has MORE than adequate capacity to haul a 23 PLUS water.
in terms of weight it's sorta like hauling 1-2 more people...
that can be used for FLUSHING, washing, drinking and so on in route.
i've hauled water 2000 miles and wouldn't have it any other way.
adequate water on board is one of the things that makes RVn pleasant.