We had our popup for 20 years with 2 kids. 1st one was 9mos old on first trip. After about 10 years, I saw a bunk storage shelf in a popup. I don't know if they still supply them as OEM, but I made my own. I don't have pics, but see attached PDF sketch.
I got some wire shelving at Home Depot. You need a piece that's longer than the distance between the upright tubes that hold up the canvas. You want to cut down the shelves, but leave the end wire long enough to go into holes you've drilled in the uprights. At the front of the shelf, cut it so the end wire sticks out a bit. Note that these shelves usually have a section at the front that bends down 90 degrees to provide stiffness to the shelf. Remember this.
Then you drill two holes in your uprights at the height above the bunk that you'd like the shelf, disconnect one of the uprights from the bunk, then slide the end wire of the shelf into the holes and reconnect the upright that you removed. The shelf will now swing up and down. Remember that section at the front that bends down 90 degrees? In my case, I installed the shelf with the 90 degree section pointing up, so that stuff on the shelf won't fall onto the bunk.
Get a couple pieces of wood or metal, drill a hole in one end, then cut them to a length that will make the shelf level. (These are shown in black in the PDF.) These are installed on the extra wire sticking out at the "front" of the shelf, and they go down along the side of the mattress and sit on top of the bunk. Note also that depending on whether you want the 90 degree section sticking up or down may influence which front wire you want to cut longer, either the one at the end of the 90 degree section or the one at the bend itself.
Works great for putting your clothing bags, etc up out of the way. I had mine about 18" above the bunk, but if you'll have 2 kids in the bunk, you may have to go higher.
The other concern is whether the bunk will still fold up with the shelf installed. In my case it did, but I won't guarantee it. Putting the 90 degree part down would help here as it can press into the bunk.
Two other comments: 1) Make sure you file down any sharp edges. They make plastic things you can stick over bare wires, too. Also, be careful you don't make holes in your tenting with the wires sticking out. I never had any trouble, but you never know. 2) The pieces that hold the shelf level can get kicked out by the kids pretty easily. I never did figure out how to prevent this. A nut on the end of the wire would work, but the wire's too thin to thread.
I installed one of these on each bunk.
1988 Coleman Sequoia - popup (1987-2007)
2012 Roo19 - hybid (2012-2015)
2016 Mini Lite 2503S - tt (2015 - ???)
2011 Traverse LT, 3.6L, FWD
2009 Silverado Ext Cab, 5.3L, 4x4, 3.73
2016 Silverado 2500HD Dbl Cab, 6.0L 4x4, 4.10