Damn I wish I still had my old boat Pamala II, it would have been perfect for that sort of thing, 38' and the majority of it deck space.
I reckon the wind angle would be a bit wrong most of the time from Cape Naturaliste and like others have said Busselton or at least Quindalup would be a better option, 50K's is a long time to be paddling mainly on one side.
It is a long cruise from Perth for a support boat though, I reckon a few runs from Rotto would be great and be a whole lot easier to organise