I don't know the answer but ...
Reading between the lines, this link
http://www.swallowboats.com/files/BayRaider_Specification.pdf gives the weight of a BR20 trailer as 500-365 = 135 kg.
That would be an upper limit on the weight of the S17 trailer (which I think is the same as my BR17 trailer). Unfortunately that's living with my in-laws at the moment so isn't convenient to weigh.
I wouldn't expect it to be a huge amount lighter because for the S17; you still need 2 wheels, suspension, axle, winch and most if not all of the supports - you are only losing 1m or so off the box sections.
The wheels are movable (using a spanner) along the frame, so you can adjust the position to get the nose weight right for your car. So you only need worry about the unbraked towing weight.
Hope this helps,
Anthony
