Nothing seemed to meet my idea of something easy to stow as well as being easy to install and remove.
These wheels are easy to make, and can be quickly added or removed when required. The eyelet bolts are permanently fixed but are small enough not to get caught up when not in use.
Step 1: Materials Part1
You will also need Eyebolts - see step 4
Step 2: Axle
Step 3: Testing the Axle
Step 4: Materials Part 2
Step 5: Fixing the Axle
With a strong sharp object eg a medium sized knitting needle (you can start with a small skewer), make a hole in the bag, put a washer on the eyebolt and poke the bolt end of the eyebolt through - this might take a bit of work but try to manage it without making a cut in the bag.
You might also want to trim the ends of the eyebolt on the inside - I'm still undecided about this.
On the inside of the bag thread the washer(s) and nuts.
Do the same on the other corner.
Step 6: Final Assembly
Adjust the spacers so the wheels spin without hitting the backpack and rotate freely when it is loaded.
Mark the end of the axle - remember to allow for the R Clip - cut to length and drill a hole for remaining R Clip.
Assemble or dismantle in seconds by removing just one R Clip - ideal for train stations and airports.
Cost (plus donated rod) = $12