Mud can fill in a cb trunk and stop the keel from dropping. Even once! (ask Adrian L) We've dried on mud a few times without grief.I saw an M on a res mooring in Bembridge, which is sandy.In Poole I've seen a nice X growing a long beard and ageing very quickly on a tod. Jose, who was with me at the time lamented on the sad state of it. Macs are lightweights and don't really appreciate being left out on the water for too long. We keep ours on the trailer and find that brilliant. Guess it depends how often and for how long you go out.. We tend to go out for a week at a time. For more frequent and shorter hops one would need a seasonal mooring.
It's pretty straight forward launching n recovering an X you know.. I've even done it single handed on a couple of occaisions, and our slip is particularly shallow so I have to walk the boat 20M off the car to get her to float!
I Guess you could keelhaul a small tarp under the boat to keep the mud out.. actually now I think of it I may even make some X-Knickers.. 6 strings cut to length (Hooks to stanchions on one side) with a strip to cover the cb should the bottom be dirty...