We've had this trike since 2004. In the early years, I realized that when placed in neutral, like when being warmed up in front of the motel while I wipe dew off, etc, it will "roll" as there is no stand on it like a bike. I've seen others wish for a hold device other than "reverse" which I also wished for (I have reverse, I just do not wish to use it as a parking brake), then one day I had an idea. I've seen /read/heard tales of trikes rolling off from garage doors, etc as the owner exited to close a door … and down driveways into parked cars, the street … even into woods. A friend once had it happen and turned to grab the trike to stop it and it pulled them down too, messed up their wrist & arm as I recall.
So, years ago … I used a piece of 3/8" aluminum 1.5" long, beveled on one end like a car ramp, and I added steps with a file. I hung it from a "ball chain" attached to the front brake hose with a zip tie. I've used it a lot, just apply the front brake with one hand and with the other, grab the wedge and insert in between the lever "tab" and lever bracket above the little button for front brake switch, release lever and brake was secure until next squeeze of the lever. I have long thought of adding a handle or something to make it easier with gloves on or just to "feel" direction if seated on the trike.
Yesterday, I made a new one. This one is made from just 1/4" aluminum, 1.75" long, no steps, just a long slight bevel on one end. Being 1/4" thick, it will fit snuggly all the way in so no steps are needed. It remains 1/2" wide, I did drill a 1/4" hole and fully countersink a 1/4-20 SS screw with a nut lock-tited and a "cap" type nut on tip. I used a little different type chain. It works superbly, immediately dropping at the pull of the lever to hang ready for next time needed.
I am thinking just from memory, that it'll work on 1200s & 1800s too, maybe others like Valks or VTX, maybe even HDs too?…. but this is on a GL1500. It's always there & to me, seems easier than messing with straps, bungies, etc. Mine, I've only used for short periods, and like I said, once set, just squeeze the lever and it'll drop on chain to be there next it's need.