We use to launch at Levington on the Orwell. Leave the boat on a pontoon mooring over night, and camp at Orwell Meadows camp site.
Great site with own club house, cheap tasty bar meals and good beer. They will also find a place for you to park the boat and trailer.
We found it easier and cheaper to book a mooring rather than pay the slip fees the following day. Just show the beer tokens to the berthing master and he will look after you