I have a TK-1 also, haven't really had the chance to use it yet but plan on taking it to Eureka Springs in June. For security I bought a preformed cable at Lowes and a couple brass combination locks. The 3/8 cable is about 25 or 30 feet long (can't remember which) with a loop on each end and has a plastic coating on it. I loop it through the wheel a couple times then run it under the trailer, loop it through the other wheel a couple times then crisscross it underneath the trailer and padlock both ends to the two tie-downs at the back of the trailer. It will be hard to drag away and the ramp can't be removed with the cable in place. I also lock the hitch with a Reece hitch lock I bought at Walmart. I have enough cable that I can lock it to a light post, or tree, or the truck in a parking lot. I wanted combination locks so I wouldn't have to keep up with a key. The cable was about $20 and the locks were $15 each. Not fool proof but better than nothing.
I keep mine in the back yard but I don't have a locking gate so I lock it up even in the yard.
I didn't use the wheel chock that came with the trailer, I bought the one from Harbor Freight and mounted it between 2 - 4ft long pieces of 2 in metal lumber (16 gauge angle steel metal with all the holes in it). I put 2 - 4ft pieces of metal lumber underneath the trailer and bolted the two together about every 10 inches or so. I double nutted and locked down the bolts so they won't vibrate loose under the trailer. I should have used angle iron under the bottom and may change it out later but I had plenty of the other stuff so I used that. That way the wheel chock is not bolted to the aluminum, the floor and those cross supports are sort of sanwiched between the strips of metal and I can adjust the placement of the wheel chock if I need to. Probably overkill but I'm like that on some things. The license plate mount is terrible so I mounted the plate to the left fender and installed led lights on both fenders also.
The ramp is a little steep at times so I use an adjustable hitch to raise the front when loading and unloading. I don't lock the tool box, I figure that is a good way to get the lid all bent up with someone just trying to see what is in there. I will fix that when the weather gets warmer though.
Pulls great empty, I picked mine up in Beloit KS. After i got home I loaded the trike and pushed it forward and back to get the tongue weight like I wanted it before installing the wheel chock.
What I did to mark the location for the chock was mark the location of the front axle straight down to the floor with a framing square, then I unloaded the trike and drove it onto the wheel chock on the driveway and marked the location of the axle straight down onto the wheel chock, then mounted the wheel chock aligning the two marks I had made. I have pulled it around some locally to make sure I have it like I want it and it pulls really good. BTW the wheel chock from Harbor Freight fits the GL1800 front wheel just fine without any adjustment.