If you have the space for a permament sink, it isn't too difficult to make one. Mine is 18mm ply initially glued and screwed together. The glue I used was one of the high-performance glues that are used from a mastik gun and dry like very tough silicon. Waterproof. I screwed at 100mm intervals all round. Then I used a 2-pack yacht epoxy. Not cheap, but seems to be absolutely fine 1+ year on. I used a standard sink drain unit and recessed the top slightly to avoid a "step" and make sure it totally drained every time.