In general, with the canister filters, you have to pull the housing in the fall, empty it out, and drain the lines on both sides. Then a new cartridge in the spring.
Me, I'd put it right downstream of the T where the city water and the output from the pump come together. On the other hand, if you're plumbing in a valve that allows you to fill the freshwater tank come together, there might be reasons to plumb it on the city water side only, under the presumption that the water in the freshwater tank is already filtered.
It is my experience that a 1, 5, or 10 micron sediment cartidge will solve most of the water problems that can be solved with a filter, provided that the incoming water is safe to drink.