> My kayak weighs 55 lbs empty. Add in my equipment for a week, another 75
> lbs. Calculate in some creature comforts and my trailer is now up into the
> 150 lbs range. Can the bike brakes handle this or more on a longer trip?

Mountain bikes (high end ones anyway) are designed to take the rider and the bike down grades that would make you choke while towing a kayak. The rim brakes or disc brakes on my mtn bikes could stop me and your kayak rig faster than any old Raleigh 10-speed from 20 years ago could stop just me. The quality and design of your equipment is what makes the difference.

> I think the jack knife/fishtail problem is caused by the trailer trying to
> pass the bike when you brake. Brakes on the trailer would greatly
> alleviate this problem. It is not always possible to use less brake, panic
> stops in traffic are not uncommon and the situation decides brake force in
> these instances.

Proper braking on a bicycle requires both front and rear brakes be applied at the same time. In order to do a set-up like you're suggesting (which I still think is unnecessary though not un-useful) would require one of your brake levers to have a double cable, so it could pull on both brakes. They make lever/cable systems like that for tandems, so that's what I would suggest. I just think it would be simpler, if you have one, to use a mtn bike with its over-engineered brakes and give that a try first.