Kristen, I know you were looking for seat padding. Concept2 says this in their marathon training suggestions: Seat: We find that variety is the key for seat comfort on long rows. Have a seat pad handy (call us for a free pad - sorry, US and Canada only) and several sheets of "bubble wrap". Bubble wrap works great for us!
I have built up up my own internal padding over the years, so do not have this issue.javascript:emoticon(':roll:')
Padding Issues
Try an old seat cushion
Bubble wraps not much use when you're rowing 2 to 3 hours in one stretch. I've found a handy old foam cushion from an unused sofa, cut it down to size and stuck on a waterproof cover and it works a treat !! 