First off I wouldn't use Prime, I would use Seachem Safe and premix it in a holding container to last 30 days max. According to the CEO of Seachem a premixed solution will become unstable after approx 30 days. Far cheaper than Prime over the long haul. In a heavily planted set up you might get away just using sodium thiosulphate, which is probably a thousand times cheaper than using Prime, Safe or any other commercial product on the market.
The guy whose tanks I linked to above tried several different methods of filtration over the years, including carbon blocks, and ended up going back to dosing. That may also be relative to ones level of chloramine, and the amount of water they are dripping each day. Or as previously mentioned if the tank is heavily planted, or not. Lots of things to factor into the big equation.
You would probably get more input in the Set Up & Filtration folder from people that run various auto drip systems, and have chloramine treated tap water.