In reply to Flat4matt: my neighbour has one, better than one I hired from a big company, but you are looking peak season so wherever you go book it soon.
You could pick it up 20 mins from Glasgow airport, contact me if you want his website details.
Just be aware that the bigger more comfy vans limit the roads that you can use, and the ferries of course. I started on Skye (as I live near Loch Lemond the fort etc.) and worked my way to Plockton Applecross .........