What's often forgotten is that car making involves hundreds of thousands, if not millions, of vehicles and the capital involved in production facilities and support systems runs into £bns. Caravan manufacturing involves production of some hundreds, maybe the odd thousand of vehicles per year. The capital involved is minuscule by comparison and the return not large enough to justify spending more. So caravan makers are left in the middle between high volume, sophisticated car production lines and individually hand crafted specialist vehicles.
I've done the Bentley tour in Crewe where they have very disparate vehicles on the line, with all the relevant bits, many unique and hand made, arriving at the right point at the right time. I also went round the Bailey Bristol factory and their Clevedon panel plant this summer and whilst they have an enormous parts warehouse and sophisticated picking and distribution system to their three production lines (caravan, motorhome, campervan) the scale and automation is not on anywhere near the same scale.