Wandering through the middle aisles of Aldi today (as I am wont to do), I noticed this £10 "festival trolley", and it reminded me of this thread, which I read a little while ago. Whilst I don't currently have need of it, this is so cheap, and looks so potentially "moddable", that I bought one.
It folds up nicely, and ostensibly can carry 30kg (which could well be more than the "nose weight" of a SIB with transom wheels). The wheelbase is a bit narrow, which might cause problems with balance, but might make steering easier.
Even if it proves not to be useful for the boat, you can't go too wrong for £10...