Mary starts her garden plants at home, then hauls the trays to the garden in a plastic drawer strapped to the rack on her Tour Easy to avoid crushing the plants in the packs. I finally learned enough to make an adapter mating the drawer to the rack:
It’s made from four layers of laser-cut cardboard glued together with crossed corrugations for stiffness. I intended make a final version from glued-up plywood sheets, but it works surprisingly well as-is and I may just make another when this one wears out.
The rear view:
The front has a cutout for the battery powering the rear camera, with the base height allowing enough meat above the battery:
The upright posts cradling the drawer may be too skinny for durability, which is why this is a prototype. The inner edges of the posts angle outward by a few millimeters to match the drawer’s mold draft.
Four feet locate the holder on the rack rails just ahead of the Ortlieb pack clips:
The rails are 8 mm ⌀ and the cutouts are 9 mm, because a little tolerance goes a long way. Similarly the tab widths just fit the available spaces beside the rail.
The two flat plates support the drawer and space the uprights to match the Ortlieb clips. I intended to mortise the plates into the uprights, but hot melt glue is wonderful stuff and the joint may outlast the cardboard. In retrospect, the outer edges of the plates should align with the inner sides of the uprights for maximum tidiness.
You don’t have that drawer and likely not the racks, so a picture of the LightBurn layout will give you the general idea for your hardware:
Cut four copies of the uprights in two different orientations, glue them together, then do the obvious thing with the plates.
The Smell of Molten Projects in the Morning 