Step 4: Add the Locking Lever
Cut the 1 x 2″ rectangle tubing into a shape that you're happy with and test fit it to your carrier body. The key to making this work is that there be a heel on the locking lever that extends past the lever pivot point toward the caster pivot point. If you get it right, the weight of the equipment will keep the locking lever held firmly in place.
Check out this video below which goes into slightly more detail. Sometimes seeing how something is done is simpler than reading about it.
Seems like a cool DIY project, but I think my definition of simple differs then this guy’s definition. The kit he talks about is about $80 for a 4 pack.