Hi Jim, a wonderful trip! We did same route in Freelander a few years ago. You'll want more time there. Don't think you'll be allowed a jerry can on the ferry.
We loved
http://www.bailenacille.co.uk/ , a bit remote and quirky certainly and not particularly cheap but a highlight of our trip, could have spent more time there quite happily (3 nts B&B £45P/P + dinner £30 in May 2009), don't think there's anywhere else to eat nearby anyway. Fabulous location, incredible beaches, sure you'd love it.
We bought a bargain Calmac hopscotch (no 23?)ticket, 5 ferries, sailed from Oban to Barra, then drove / sailed with stop offs all the way up to Lewis, then ferry from Tarbert to Uig, down to Armadale to Malaig.
I found it a juggle to arrange between booking ferry crossings and finding accommodation to suit. It wasn't an option for us but I didn't see much opportunity for wild camping in that there seemed to be a lot of roadside fences.
There was a cafe on the pier in Castlebay that served fabulous curry. Nigel