Brodes - What panniers or bags are you using on those racks?
I bought the Oxford off-road pannier bags (can't remember what they're called, but they are made for dual purpose use - waterproof, don't have zips, come with the built-in straps to secure them to the pannier frame, etc) also from Martin (Man on the Moon).
Were more cost effective than some of the competition (I considered a number of options before deciding on these) and presented the right combination of quality, price, size, functionality, etc to suit my needs. Was very impressed with their performance on the trip to and from the NW bash - didn't budge, even on the fairly long corrugated dirt sections, zero dust ingress, etc.
My apologies for the poor quality of the photo's below, but they weren't taken with the intent of advertising the Oxford pannier bags. The stuff on the top rack is my tent, tools, crocs and sleeping bag - looks a little like a Moriah bus, but it worked for the weekend trip. I still plan to buy a 40l ATG bag for the top rack to keep everything (tent, sleeping bag, etc) dry and dust free, but that will have to wait for my Xmas pressie.