Here's what we use in our office:
We have two OLD laptops, which sit closed, running, on top of the file cabinet. They're running VNC server, so they can be remote controlled. When we want to access AC remotely, we use VNC viewer to remote control them. If the connection goes down, we don't loose anything. Our internet speed isn't that fast, and even with a slow connection, this works very well, with no risk of lost data.
VPN is SLOW.. and the data access scheme used in AC is slow, so BOTH combined would make VPN a difficult solution to use. The laptops are cheap compute servers - you can get a used machine on e-bay for well under $200. It also has the advantage of being able to see what the remote user is doing if you want/need to (ie, just open the laptop and look at the screen!) and of being backup to the office computers if worst-case a machine goes down.
V.
