Thought I'd flag this up as generally more small boat stuff there than RIB's.
Kent Boat Jumble
Went last summer and not too bad, always great for picking up ropes, tanks, fenders, skis, LJ's, small items dead cheap, sometimes small SIB's too. I even bought a Tohatsu 9.8 last time I went.
It's not massive (and not sure how many sellers will be there this time of year) but worth a look if you're local.