You have to be kidding me!
What do you do with so many tapers?!?! 
Motorcycle trailer
I picked up a used motorcycle trailer. It already had 2-foot high heavy plywood sides held up by welded iron. There were “eyes” welded all over the place to tie down the bikes and a big iron rail down the center, adding weight.
My big addition was a raised crossbar of 2x4 fore and aft. I bolted them onto the trailer and used eye-bolts on the bottom to give me 4 connect-points low and inside. The crossbars are high enough to slide 3 SOT kayaks into the 4x8 bed on side.
The tongue is about the same length as the HF trailers and I have carried 2 15’ kayaks on the crossbars, longer might be pushing it.
So far, the biggest load was 6 kayaks. No problems, very little bounce.
Trailer
I modified a 4X6 trailer to carry two kayaks upside down. Works excellent and all I need for tie down is two straps. The carrier is removable so I can still use the trailer for general use.