Here's how I converted my Sportsmobile's clothes-hanging closet to one with shelves and bins. This opened up a lot more usable storage for clothes and other items. The bins are super-handy, and it's easy to take them into the house to pack and then just carry them out. On occasion we've even taken them into a hotel room at night like a suitcase.
Pics tell most of the story, but here are some notes:
1. I used low-profile shelf sidetracks (aka "standards" or "pilaster strips") on the inside walls of the cabinet. Like this: https://www.lowes.com/pd/Style-Selec...-Strip/3006365
2. Adjustable shelf pins fit into the track: https://www.lowes.com/pd/Style-Selec...f-Pins/3006364
3. The shelves are 1/4 underlay plywood to maximize available space. So far (2+ years in) it's been plenty strong enough and has not bowed, mainly because the space it's bridging is pretty narrow. I cut the wood tight from cabinet side to side, notching it out to accommodate the siderails. At first I only cut the shelves to fit between the rails, but I found they were much less secure. The tight fit keeps them in place when the bins are pulled out, etc.
4. I custom-made bins to fit the space. Each is mostly equal in size. We travel with three people (me, wife, teenage son) and we each get a bin. You'd be surprised how much you can fit in one bin! The bottom two are mostly square, while I had to angle the back of the top bin due to the sloping sidewalls of the van.
5. The bins are made out of coroplast sheets repurposed from roadside political signs after an election :-) At first I just did one as a proof of concept, but then I went and priced new coroplast sheets ($$) and decided to just make them all from the recycled signs. Gorilla Tape is used inside and out to secure the sides. They have held up very well so far and are easy to slide in and out. The relatively thin, but strong material maximizes usable space. I was going to cover the bins with contact paper or something to make them look nicer, but I'm cheap and nobody sees the bins anyway with the doors closed. (Although they are a constant reminder of the discord around COVID lockdowns so I may end up spraypainting them.)
6. There is a small bit of wasted/unusable space at the top of the closet due to the way the closet is constructed (the CO2 detector was originally in this space). At some point I may hinge the top cabinet face and make it a small storage cubbie with a floor, or possibly a drawer.