Would welcome advice from seasoned travellers with luggage, as we prepare for our first longer trip in our Plus Four.

From the many great suggestions on this forum we picked a wheeled waterproof duffel bag from Ortlieb for our rear rack (side panel storage; no spare wheel) and we got a couple of thief-resistant Kanulock straps.

What do you do to strap the luggage on so it cannot take its own surprise holiday on the motorway tarmac?

Is it enough to have a cross arrangements (one vertically in the centre + one horizontally)? Do you loop the straps around the bars at each end or just once around the whole thing (luggage+bars)?

And do you put anything under the bag to protect the chrome bars from scratching?

Thanks for your advice.