Let me preface that in all the years that I've been riding URALs, not one instance of theft has occurred.
Having said that, I prefer to keep honest people, well, honest by locking things whenever possible.
Real thieves, if they really want in, will get in.
Anyways, today I installed a couple of flat corner braces from the hardware store ($3) to the lower back of the seat back cushion in the sidecar to prevent it from being removed from the inside of the sidecar. It's designed to be removable you see, a fact not known by many folks.
Removing said seat back, even with a newer Ural's lockable trunk, obviously bypasses the minimal security provided by locking the trunk lid itself. Now, that's not easily done on Fiona:
The upper edge of the seat back came with two metal tabs that prevent forward movement. Everything depends on your being able to pull up the lower edge of the seat back, now it's not easily possible.
Lower left corner of seat back
Lower right corner of seat back
I had also recently added a tow hitch lock to the trunk on Fiona. It prevents easy movement of the handle which is used to secure the lid of the trunk on the sidecar
Unlocked position, the handle can pivot upwards to release
the hooks which hold down the trunk lid
Right: locked position, handle cannot pivot upwards to release the hooks.
The above idea I got from a posting on sovietsteeds about securing the older model year trunks. There's many ways to do it, this is just the one that struck me as simplest.
In areas where my paranoia is really active (areas I'd tend to avoid anyways), I also carry a bike chain/cable that loops around the spare tire cargo rack, spare tire/wheel and part of the subframe.
A different and very temporary mod is the addition of a small "Slow Vehicle sign" sticker to Fiona's spare tire rack. Just a visual cue for the cager who might come up behind me and not realize that I'm only going 40 mph for the next 1500 miles or so as I break in the rebuilt gearbox on Fiona.
Do you think they'll notice, and get a clue?
Lastly, the stock position of the mirrors that came with Fiona were not good for my being able to easily see to the rear of the rig while driving.
I got these extenders from amazon ($17) which raise the mirrors 27mm and extend them outwards by 40mm. The mounting screws they come with were too short for Fiona's application, but I had some onhand which did the trick for now.