I built one for my buddy in Klamath with plans to mass produce. Unfortunately to become a manufacturer is not cost effective. The one I built could be used to double stack without the boats touching each other and still be able to remove the lower boat amd put on the dolly by yourself after you remove the top boat. The standard laser trailer is a o.k design but too lightweight tires are to small and suspension sucks. The one I built used 12 in tires torsion bar axle. I can build you a custom but you have to register it as a special constructed vehicle at DMV and they put a vin on it
With my design time build time and parts 3500 to 4000 . There's about a 3 mouth wait time. I have the original jig in my shop..
If I were looking for a good low cost trailer I would pick up a ride on or convert a small boat trailer.