We purchased our van on the 22nd December 2010, and took it to a local beach about 40k down the road and set it up on the 24th Dec. We then drove home for xmas day with a plan to return to the van on boxing day. It p!ssed rain all christmas day and night, we were woken early boxing day by friends telling us that the awning had collapsed. $3000 and luckily an insurance claim later and we were sorted.
I have 2 recommendations, if you expect a bad storm roll the awning away - however if this is not practical (ie you have a full annex set up etc) then make sure you have plenty of roof rafters installed as well as a good antiflap kit. We use the Aussie Traveller flapkit and rafters and have found them easy to use and well made. I also ensure that the outside of the awning is as low as possible to ensure good water run off. I also put the awning legs just off the slab and secure them into the ground with a tent peg through the hole in the foot. I have an 18 57 6, which doesn't have the world's biggest awning, so I use 2 rafters - Anything longer and I would have 3 or more. I asked the dealer when we originally picked up the van if we needed the rafters and was told that it was not big enough to warrant them. After it collapsed, this was the first thing we had installed along with the new awning and have weathered some big downpours since with no dramas at all.