The Hebrides

This june we plan to go to the Hebrides. We would very much like to get some advice about the possibilities there are for camping with a 5.70m motorhome; do we need to make reservations for the boat, we rather won't because of lack of freedom. And is it worth while to go from Oban via the smaller islands to Lewis or are they all very much the same?? I realise that it also personal whether you like something or not, but I still would very much like some advice! 

Jetske Graatsma, the Netherlands