I've got mine in a covered 25' slip for $95/month. I had to wait over two years to get it. Before then I bet I burned up at least that much fuel hauling the boat up to my house (1,100 ft. climb in 3 miles) during the busier months. It is also colder and wetter at my house despite there being a metal shed for it. This brings increased condensation & risk of freezing. During the salmon season, a guy can spend an hour in the launch line when putting in and again when pulling out. It makes for a long day. With no wait with the slip, there's more time fishing and it is easy to duck out quickly in the spring and fish for a coupla hours after work, or take my wife for a quick ride, something harder to do if the boat is at home on the trailer. Also, with a slip you have don't have to deal with the yahoos and jetskiers at the ramp who don't know what they are doing (like making everyone wait on them while they try to learn to back up or load their boat on the ramp or leaving ithe boat there, blocking the ramp while they go to find a place to park).
The hassle of a slip? You have to remember what is in your boat and carry what you need to it, instead of having the luxury of loading & unloading it at home. (I keep emergency gear - backup rods, food etc. onboard). Also, if your trailer sits unused, the bearings and light connections are more likely to rust/corrode. Boats in water experience more electrolysis, and, as mentioned before, if the pumps are removing rain or leakage water... they will run down. Mine has a solar charger on the roof which minimizes this. And, again, those moorage fees in the off season would buy a lot of gas during the time when most folks use their boats. But I use mine year round, partly because it is so convenient. C.W.