I have done a bit of work on my Brompton which I need to finish off this weekend. I find the bracketry that holds the rear mudguard is not really up to the job when the bike is folded as the weight of the bike is transfered through the fragile plastic mudguard. My original mudguard disintegrated after a while, I think it is particularly proneto damage when slinging it into storage spaces on the train. I have made a heavier duty bracket which supports the weight of the bike when folded without it being transfered through the mudguard itself so it should be much more resilient A pair of luggage wheels replace the silly little jockey wheel making it much more and you can actually roll it as intended and with much more ground clearance, which you normally need the full luggage rack for. It's a bit agricultural, if you are into weight saving you might want to look away. But, it's proof of concept and if after a bit of testing I am still happy with it, I might design something a bit more refined and get a local fabrication company to make a neater job of it.