Enjoy your trip.
If you decided to go to Skye using the ferry from Mallaig, my advice would be when leaving Skye, do it by the Skye Bridge,
(Ferries in Scotland are quite expensive and unless totally necessary are best kept for using on the short ones that can save lots of fuel,
some ferry trips mean missing many road side places you might want to visit.)
Maybe the best way is VIA Fort William to Torridon & Shieldaig, Applecross & Skye and leave by the Ferry to Mallaig.
http://www.calmac.co.ukie The Corran Ferry,,
You might take this 6 minute ferry if you were not going into Fort William,
*You will pass here if you come through Glencoe or come down from Oban.
but most likely you want Fort William & Ben Nevis.
Yet taking the Ferry takes you onto wonderful places & routes.
Saves driving around 30 miles to get to the other side.
(I preffer using this ferry as i return South after i have been nothwards)
http://www.lochabertransport.org.uksee ferries.
Well worth when visiting Applecross or the 'Bealach Na Ba' from the first reply,
to go to 'Sheldaig' & to Torridon.
http://www.undiscoveredscotland.co.uk/shieldaig/shieldaig/index.html*I would fill up with fuel & food when you have the chance and carry spare fuel.
places like Shieldaig will often have only one Hotel/Pub, no shop & no filling station.*
Different times can be very different, but fuel stops can be some distance if one you were counting on is unavailable.
Many many pretty special places to make a visit to on your return trip,
depends on if your route is back by Inverness or to Fort William.
Google
'Road to the Isles' & 'Silver Sands of Morar'.
'Undiscovered Scotland' is quite handy for info.
http://www.roadtotheisles.co.ukhttp://www.road-to-the-isles.org.ukCamping near here. Worth a night someplace in Glencoe or before Ballachulish IMO.
I would go on a trip like yours VIA Glencoe.
http://www.clachaig.comWorth a night just down the road from here.
http://www.redsquirrelcampsite.co.ukThe 'Scottish Midge' will be your August problem possibly.
george
http://www.youtube.com/watch?v=CV5mh4SbjWs