I have spent a lot of time on the Island and know the Island quite well.
Southlands was a great site and as long as the CC don't play around with it too much it should remain so. Down side is that the buses are infrequent but then all Island buses are infrequent.
The Island is not a place for large MH to cruise around. As soon as you turn off the main roads the lane become narrow and rough. I like to think that this is the local council's way of controlling people's speed. I used to know coach drivers who work on the Island. They have an unwritten rule in that all tourist coaches travel in an anticlockwise direction around the Island. That way they are unlkely to meet another coach in a narow road head on.
Nowdays, I hire a cottage. Much easier. The Island is one of my favourite places to visit but unless you have a small MH, are happy to hire a car or have a scooter you will have to stick to the main roads (bus routes basically).