Dream,
A couple of comments about the mold situation. Do you know that the Sunbrella upholstery covers will zip off (for the most part), and you can wash them in a machine, with mild bleach solution, and a soap such as Woolite. There is a 303 fabric spray which will then make them waterproof again. This will allow getting rid of any mold spores in the actual fabric. If mold is in the foam, that would have to be replaced.
A good cleaning with bleach, should help with any mold in the water tank--and you can go with a fairly concentrated solution there. If there is any "crud" in the tank, you can put ice cubes in the tank, and then take the boat for a spin--the cubes will act as a mild abrasive material to help clean anything on the tank walls. It is a good idea to vary the water level as you do this.
Unfortunately many municipal water systems will have some degree of algae contamination. Something to keep in mind. Usually the chlorine will be enough to suppress or kill the algae. This is one reason, we do not pre-filter, and remove any residual chlorine when filling water tanks--and we do add small amounts of chlorox to the water tank, if there is any question about the water source (as in many remote areas).
Of course your safety is most important--and there are many alternatives for the drinking water. We re-use the water bottles, and often freeze them to use as a coolant in the ice chest. (thicker bottles are better, and gallon bottles are excellent also). We also always use a Brita filter on the tank water, if we drink it--and that helps to remove the chlorine taste. However, one needs to regularly clean the pitcher, and replace the filters. There are better filters for removal of bacteria, spores, and parasites than this pitcher type of filter.
So great you can live out some of your dreams!