@ai6yr Oh, it was no problem at all! I cycled for about 45 minutes with this setup, from Den Bosch to Rosmalen, overal several steep bridges and messy city center traffic layouts, with plenty of bumps in the road along the way. It never even threatened to fall off 🙂

There's a surprisingly amount of stability you can achieve with criss-crossing bungee cords! A particularly useful trick is to hook the end of one bungee cord onto the middle of another; that way you permanently tension the other one while also pulling it towards a particular direction, so you get a very robust sort of triangle arrangement.