I used a conventional aluminium rod waterbottle rack and mounted it on the right vertical frame tube at the front of the rear rack, with stainless steel worm drive hose clamps. This puts the bottle inside the triangular area between the seatpost and the rear rack on my 2018 Radwagon. It sits above the motor controller but does not touch it. The only waterbottle mount on the Radwagon is under to lower frame downtube and is too close to the front fender to allow a bottle cage to be mounted there. These threaded inserts do work for some types of air pimp mointing brackets, so are still useful.