I don't have any first-hand experience w/panniers yet, but, for my mini-velo that has much longer chainstays than any folding bicycle, I'm going to use a Racktime Foldit Fix rear rack for 20". Another rack-specialty company to peruse is AltanVelo. They seem to have a relatively large selection of racks for 20". There's also the Tern Cargo Rack. I can't confirm that any of these will afford enough distance of the panniers from your feet. I think all 20" folding bicycles I've seen w/panniers are using taller racks, originally meant for 26 or 700c wheel bicycles.