Confession: My van is a PM. However, I have learned a lot from this forum and would like to give back. My shower stall is not van-specific: it will fit anywhere you have space and four hooks on the ceiling.
The superstructure weighs less than a pound and goes up in less than 15 seconds. The fabric is 2.2 oz ripstock nylon. The attachments are plastic rings on straps of 3/8" grosgrain ribbon. On the opening side, I put grommets in the straps and pushed them apart with a short tent pole. My resulting structure is 2' x 3' at the top.
The sides taper down to fit inside a 15" x 18" x 6" bus box (for clearing restaurant tables) that I found at Sam's. I made an insert to fit inside the box out of netting material, then sewed the bottom of the fabric to the netting. When I put a plastic grate in the bottom of the box, the fabric is held tightly and cannot come out.
I cut down a plastic cutting board from Walmart to stand on over the grate. Water flows over the edges of the cutting board down into the grate area.
The "door" opens inward and is not tapered. It provides enough coverage for the wand from the Helio to snake through.
To close (or open) the door, I put its ring on the outside of the rod.
Before removing the bucket, I raise the bottom of the superstructure by its center ring, this containing most of the water in the resulting "doughnut."
The superstructure can then be moved to the doorway to drain/dry.
For storage, everything fits in the box with room to spare.
Analogy:
If I hang a tarp and put a bucket under it, I have no reasonable expectation the inside of the bucket will stay dry in a rainstorm. No matter how tall the bucket, wind could lift the tarp. If I stake the tarp so that its sides are held taut, it becomes a tent fly and the bucket becomes an inner tent. My shower stall with its taut firmly-held sides is an inside-out tent keeping water in instead of out.