The trailer in your sketch looks like it'd be an absolute beast to try pull on a windy day, unless you built on a heavy trailer frame, which would then require a heavy enough tow rig.
If it were me, I'd think about building the kayak storage separately.

For what it's worth, here's a picture of my trailer (photo credit - Ted Henry). I built it on a 5X8 tilt bed trailer I got off of Craigslist for under $300. I put on a new tongue that is about 6 feet longer that the original. The lockable storage is very handy. It sure beats loading the boats onto the roof racks of our big van.

-John

: Wanted to toss this out before I trash the idea. The more I get into this the
: more I am not sure it is worth the effort or would work the way I wanted.

: The idea was a lightweight SOF trailer to haul and store kayaks in. Biggest
: advantage of an enclosed trailer was the fact I store them inside. Come in
: off the water tired and not have to unload. And of course the easy or
: loading a boat in a trailer as opposed to overhead on a tall truck.

: Here is couple of sketches of what I have come up with. Trailer is going to
: have to be 20 feet long. The doors have been a major problem to come up
: with a workable idea. I think these bi-folding doors would work just fine.
: Just tie them off with bungee cord when open.

: The sides would need to be sheathed with plywood. The top would probably need
: to be sheathed in plywood too. All this starts to take away the advantages
: of the SOF idea. Weight starts to climb, etc. I guess I could use some of
: Platt Mumfords ideas from his boats. But, I am really starting to have my
: doubts about this idea. Just not sure it is worth the effort and not
: convinced it would be rigid enough either.