Not sure if you still need a solution but here is one that worked for me.
My requirements for a trailer include trailing a track motorcycle, moving furniture (kids in shared houses) taking rubbish to tip etc - usually you would buy a box trailer for all that but they don't in standard format take 2 AI's do they? Not big weight but stuff too big for the car.
Got a quote for a custom trailer to do that - AUD $4,500 - thats a third AI !! - no way.
Solution from Mark at the friendly Hobie dealer (who has done a variant on this himself) was an imported Chinese trailer kit - he recommended Carlex Easy Trailer and so do I - see web site at -http://www.easytrailer.com.au/multifunction_trailers.html
I suspect they or their mates are or will be shipping to pretty much most Western countries.Major Point
- if the trailer is going in a weather protected place you can go with ordinary paint finish (red bits in the photos below) - if the trailer will be left out in the weather for extended periods or you need to immerse it (not usually needed to launch Hobies) you will have to get a galvanised version.
So ordered a 5' x 8' folding trailer with a wooden floor to bolt a bike track and carrier to - on reflection would not have asked for a folding trailer as not necessary for me but it may suit you if your garage space is limited.
Arrived in boxes in about a week - cost about $950 delivered as I recall. The design is approved with our roads authorities in all Oz states and apart from having to have it inspected registration for on road use was cheap and easy.
Built it in about 8 hours - a second trailer would take half that and would also quicker if you had a good helper (the dog just laughed at me) but I went very slowly and had to read the manual as a lot of the bolts and fittings needed careful sorting - an ordinary set of socket wrenches and spanners were all that was needed (no welding or drilling).Second Major Point
- You will need a trailer shop to do some modifications to make the trailer suitable for kayak transport - I had the local boat trailer guy build two H frames to bolt on (removable) to the frame of the trailer and also to install an extendable draw bar when in kayak transport mode - an AI is about 16' / 5m long and the mast is longer again so you need more length to clear the towing car and not hang over the back too much (they can book you for that here). Time for pics to explain -http://www.flickr.com/photos/25510729@N03/4212389096/
The red frame and the wooded floor came with the kit - the galvanised and removeable H frames and extending draw bar are custom bits.http://www.flickr.com/photos/25510729@N03/4211626225/
From the pic you can see the extendable draw bar (retracts when using it as a non kayak trailer).http://www.flickr.com/photos/25510729@N03/4212389550/
Note that you need to extend the wiring harness to cope with the extended length of the draw bar.
A view of the mods to the A frame to take the kayak supports -http://www.flickr.com/photos/25510729@N03/4212389394/
Cost of the mods was $800 and a fairly simple and quick task for a trailer shop.
Bought some square foam rack protectors to put where the AI can rub from the local foam discount shop and used some thick zip ties to secure them - going to roll a layer of astro turf as well over them as the foam is soft and astro turf is easy to slide plastic boats on - here is a shot of the foam tubes cut and zip tied into position -http://www.flickr.com/photos/25510729@N03/4212389712/
Things still to do - Will need to re-position the number plate holder (catches your leg when walking around the trailer) and want to replace the conventional trailer lights with LED units (water proof and MUCH brighter). Still debating about putting the mud guards back on - think it looks better without but may not be so smart in the wet.
Oh and a last idea - now have 2 AI's (wife demanded equal fun) so the ancillary bits (Mirage drives x2 , dagger boards, PFD's, tramp, INOX drive lube, GPS mount, water bottles, paddles, tools etc) all need to be carried on the trailer n'est pas? - my solution is a large 90cm x 35cm x 35 cm nylon travel bag and all of that gear fits in it and just ties on to the trailer - spent $120 but it has wheels and re-inforced base so I think it will last well - a layer of bubble wrap protects the drives - bag with all of that in it in the pic -http://www.flickr.com/photos/25510729@N03/4212389834/
Have also got a good solution for safely and easily hoisting an AI under the ceiling of a garage or car port - but that's another post for another day.