On our last houseboat, we used the boat year-round, dock water was turned off for 4-5 months.
I built EXACTLY the system you describe. 5 micron prefilter, UV chamber, .5 micron post UV filter. We were on an unbelievably clean north Arkansas lake and used the system 2 winters without anyone even having a tummy ache.
I would retain the storage tank and pump into it though, those .5 micron filters REALLY slow flow (means just about any UV lamp is gonna be enough though). Don't remember the model # but was using a premium on demand type pump and I can still pee faster than the fininshed product would flow!
I carry a gun because it's too tiring carrying a cop.