I made all the brackets using my lathe and milling machine and I am in the process of anodizing them black. The mudguard wheel bracket is just a piece of bent aluminium plate but the grade of ally is too soft and it bends too easily so I am thinking about an alternative design. This wheel is not a true castor, its fixed in place and can not swivel in the way a castor would. I thought long and hard about a proper castor but decided that with the four fixed wheels on the rack it would be of no benefit as the bike can not turn on the spot.
The seat post height can be set so as to use the seat as a handle to pull the bike along, similar to the Brompton. I can imagine rotating the seat and using a seat post mounted rack would make a good trolley and if rotated slightly more towards the rear wheel (when folded) would help the stability, especially the front mud guard stand is not be lengthened to suit the height of the skate wheels. I would like to use the slip on cover with the bike but I dont know if the seat can be passed through the top of the cover to be used as a handle.