Come the new codex, and the changes to HWTs that went with it, I simply use the removable guardsman as a wound counter - if the team takes one wound, the gunner comes off, and if it takes a second, it's dead.
To do this I simply used some 3mm x 1.5mm rare earth magnets. These are small enough to fit in the bottom of Cadian boots, and so one goes in there and the other on the bottom of the 60mm base. The gunners are held in place by the basing material, which is placed around their boots.
Here's a couple of pics to show this. (Sorry they're a bit blurry, I took them a while ago before I had a tripod for my camera):
In the top picture, if you look closely, you can see the footprints in the sand that keep the loader from swivelling around. In the second you can see the magnet embedded in the bottom of his boot.
So there you go - simple, and an easy way of keeping track of those wounds!