|Using a second router isn't likely to improve things unless it has a much more powerful antenna.|
If it were me, I'd look at some external antennas that could be attached to the system in your shop, but mounted outside. Something like the following may work for you:
If that doesn't work, you'd likely need to go to a pair of point-to-point wireless antenna's. Something like so:
FYI, the above link is just the first one that came up. I've used some EnGenius equipment and been quite pleased with it. I suggest looking through what they have to offer. They probably also have the "booster" or "extender" antenna's I mentioned above.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.