I investigated this at one time. You can find out a lot of information simply by using google and doing a search on rotomolding. Basically polyethylene pellets are introduced into a precisely temperature regulated mold which is rotated on all axis(es?)until the pellets melt and are uniformly distributed. As can be imagined the equipment for this would run from expensive to more expensive, to VERY expensive. I determined that it is not my cup of tea and will continue to build one boat at a time. Good luck.