You need a couple of metal struts to keep the pannier off the fender & wheel. The yubabike shown left has the pannier supports integral, also a couple of foot rests. I had to add a strut down the middle of the right footrest to keep the yuba pannier up off the derailleur take up, else I couldn't get 1st and 2nd speed.
The ride one up 500 picture bing found me had an optional book rack but the support strut ran forwards towards the seat stem area instead of down to the rear axle support flange. that would do nothing to keep a pannier off a tire. To keep stuff off the tire I welded up an entire metal basket for my Pacific MTB, but it was heavy. Main strut cut out an aluminum door ran straight down to the fender mount on the rear axle flange. Really Yuba did a much better job out of aluminum, much lighter.
The best deal to avoid rubbing is a Wald basket, but many bikes don't have any support for the front clamp but the seat stem, and that allows the basket to wiggle from side to side. Some bikes have holes for a basket mount in the yoke that runs down to the rear axle flange, but most frames don't these days. The ride1up rear yoke looks particularly stripped down. The days when every kid mounted newpaper baskets on his bike are over. You have to pay extra for cargo capability.
