I agree with Deliberto when it comes to making them; however, I've seen a few buildings that already have these installed. Heck, I have one installed above my garage entrance. Anyways, what I'm getting at is that maybe we could find houses with these already installed, take them down, and install them elsewhere. I actually have no idea how hard they are to build from scratch, but I do know they are fairly easy to assemble and dissemble. They could be portable. Realistically though, it would be fairly easy to find this at the in-game warehouses, garages, businesses, and logging mills. I used to rent a storage unit that had one of these installed on each "unit block", they were used to deter thieves, vandals, animals, and just about anything else with something to hide. (Coincidentally, the storage unit I mentioned was located in Kentucky. )