Dan,

Surf to Summit has a very nice selection of seats and backrests, both together and seperate.

Keith,

for the Spray Skirt, I would recommend Seals.  I picked mine up @ MEC.CA, they have a really good return policy so if it does not fit, you can always return it.

I have issues with my lower back and my wife sometimes has leg pain from sciatica.  I replaced my Canondale mountain bike seat with an anatomic gel seat a few years ago and it made a HUGE difference.

For our MC 16.5, I'm going to try a couple of gel seats like these.  They are 1inch thick:  http://www.austinkayak.com/products/684/Skwoosh-Kayak-Seat-Cushion.html

http://www.austinkayak.com/products/685/Skwoosh-Extreme-Kayak-Seat-Cushion.html

 

I used the seat that came with the LT 16 (tractor )  for a while but found that although it kept me low in the boat and stable, i began to get numnbess from sitting too long.  I finally took a block of the dense closed cell foam, cut notches in the side to fit around the hip braces, sliced a long wedge off the bottom of each side to match the slant of the bottom pannels, and cut a groove down the center bottom to let water drain through.  Then I sat on it and sort of traced the shape of my but and started carving away with a knife, and then with a "sharkskin" rasp, and then finally with coarse sand paper to get the shape of me molded into the foam, cutting as deeply as possible without comming out the bottom.  I now have a very comfortable seat that almost never gives me nerve problems.  I wish I had the link but several people have posted more detailed explanations of this process.  Mainly trial and error until it feels right.

 Ed