Another consideration that would need to be taken into account if someone were building a trailer is that you would need to be certain of the number of kayaks and gear it would normally be hauling and especially their weight. I have a heavy duty 8 foot trailer that works great when loaded with 2,000 lbs. of dirt or gravel. But if I try hauling some light furniture or moving someone's boxes, it bounces so bad that anything in it will be busted up or damaged from the trailer flying up in the air every time I go over a bump in the road. Heavy duty shocks are great when the trailer is loaded with a lot of weight, but terrible with a less than full load. With kayaks, you could get some real damage to the yaks from the bouncing or even have the trailer flip over when it bounces over some bumps in the road. It would need to be carefully matched with the normal weight it would be hauling. Also, need to be carefull with it not becoming top heavy or subject to wind flipping it over at higher speeds. If a trailer flips on you, not only would you destroy your kayaks but would also wreck your vehicle and injure yourself in the process. And even if you weren't hurt, that would end up costing you a lot more money. So any "homemade" trailer would have to be carefully built and engineered properly in order to not bounce around too much. I would also go with larger wheels on it. Personally, I think that I would stick with a factory built trailer made especially for hauling kayaks. That said, I have a friend who built & welded up his own trailer (that he uses for hauling 6 canoes and their gear) and in 16 years he has never had the slightest trouble with it, even when running on curving roads along rivers and on the interstate highway. So it is doable if you know what you are doing.