Neil F wrote:When the ground had a slope the bike would fall over.
FWIW, I've got a partial answer to that one - a "handbrake". I use a velcro strap to hold the rear brake on, which stops the bike running away and lets me point the bike up (or down) the slope so that the bike leans at the optimum angle. It can sometimes be a bit fiddly to find best direction to point the bike, but this trick does work most times. That said, I haven't tried this with more than 12kg on the rack because I'll use the trailer for more than that.