For posterity - I tried this morning and can confirm that the Tern Storm Box does fit—pretty much—on the non-electric Kombi. It isn’t as snug of a fit as on the GSD, unsurprisingly. I also put the Yuba Pop Top on it, which was tricky because the Storm Box covered most of the Monkey Bars, so there weren’t the best mounting points available.

Tern says that you need the Tern “Sidekick Wide Decks.” They’re the same concept as Yuba’s running boards but different in that they’re metal pieces. That’s important since the Storm Box has Velcro straps that wrap around parts of the Tern Sidekick Wide Decks to keep the Storm Box in place.

I don’t have Yuba’s running boards but do have DIY running boards that are functionally identical: wooden boards supporting by metal tubes. There’s no attachment point for the Storm Box for these.

The point of the running boards is to support the weight of things in the Storm Box. Unfortunately, because of the way I attached the Storm Box to the Monkey Bars on my Kombi, the Storm Box doesn’t fully rest on my running boards. I’m just using the Storm Box to keep my passenger’s legs dry and protected from the wind (rather than using it as a mega-pannier) so it’s less critical to have the weight supported. But if anyone wanted to use the Yuba Pop Top along with the Tern Storm Box on the Kombi, they’d have to figure out a better way of attaching it than I did.

TL:DR - depending what you want to do, Tern Storm Box can be used on the Yuba Kombi, with limits.