I'm not surprised it looks like an absolute stinker tomorrow.
It is indeed, pishing down! On the bright side, it should drown the midges, for a bit!
Currently in the Trossachs but it looks like Barra and Vatersay won't happen as our CalMac ferry from Mallaig to South Uist booked for tomorrow has been cancelled.
As an alternative, you could head for Lochaline or Kilchoan and cycle around Mull via the ferries from those places. How big did you say that camper was ... Oban might be a better bet?
https://www.calmac.co.uk/article/2165/Mull