Thanks all, some really helpful advice in this thread that I will inwardly digest and action. I must admit that I don't use my tonneau a huge amount at the moment but for this trip, with only me and my kit int the car, including golf clubs in the passenger footwell, it could work well.
Graham, on your last comment re Ardnamurchan, we absolutely love that part of Scotland and are going to an amazing house we rent for the third time for our family holiday this year called Bunallt Eachain. Fantastic views and location and all one level for my better half who is in a wheelchair.