My kayak trailer attachment is a bit simpler: just a cord that ties the bow directly to the rails under the bike seat. The trailer itself is a kayak/canoe carrier that I bought from LL Bean quite a few years ago.
With the single kayak this arrangement only works with my Bike Friday due to the need for lots of room between the bike seat and the rear bike tire. But I can tow my double this way with my regular road bike as well since it has a shallower bow profile.
It tracks well and is very stable even on fast downhills. Of course the weight of the boat and trailer do make climbing the hills considerably slower than normal. One of my closest reservoirs for kayaking involves a climb and descent of about 1000' so I get to experience both characteristics regularly (but I don't take the double over that hill by bike).
