I've done it in the Westie for the last 8 years - including the wet one, and with no.1 son as passenger, taking two tents, sleeping bags, tools, trollies for a week, wok, wedge and passports. The trick is to use lots of bungies, fasten stuff to the roll bar, have a bag under your knees and drive steadily.
I've now reached an age where next year I'm taking a bigger tent ( courtesy of the Decathlon sale ), and a small saloon as I'm not likely to indulge anymore in the Friday antics at Houx or Arnage, and I want more space to bring the crates of Muscadet back.
My matey, takes his Westie and puts a microfridge for the cold beers in the passenger seat.
Go for it - where there's a will there is a way.
Regards
BryanC