Hello Craig,
Roger has it about right, though I would add that all to frequently, caravan manufactures choose to develop a product or part for the caravan market that alrady exsists in the domestic or commercial market.
When you consider the disadvantage and cost of the excersise, the "own Design" component often fails to deliver the expecetd performance, and is frequently less durable, or has some other acheliese heel, which has already been designed out in the commercial/domestic product! I cite water pipes as a prime example. How many caravan have suffered tainted water, blown coulpings, faulty taps/switcehs etc?
I suspect that if a caravan was repiped in plastic domestic domestic grade pipe, the weight gain would be relatively small, and the cost would be less becuase of the volume of product commercially available. - replacements (if needed) would be off the shelf from most DIY stores.
Similar stories for electrical fittings, but some Caravan manufactures still go for the expensive specials.
As Roger points out, if a motor manufacturer were to get involved in caravan design, then we would see big changes, Doors and windows that fit properly, locks that offer some real security, lightweight structural engineering to reduce weight, areo dynamics properly considered, development of superior braking systems to name a few.
This would be achieved by more consistent design and manufacturing processes. Did you know that most caravans are manufactured by part-time emplyees working on a piece rate system which does not encourage quality workmanship, and most vans are buit in only a 6 month build season.
The industry does need kick start, because I am sure that far eastern countries are showing and interest in the European caravan market potential, especially those who are finding the attraction of increased consumer choice and spending - never mind the 9 million cycles in Bejing, consider how many cycles are being exchanged for cars, that could tow a caravan. - And the Sweedes will launch thier own low cost self build van in the near future as soon as they can find enough allen keys?