I found these guys in a bits box at a local game shop. I also used this opportunity to try out the Steel-Catwalk Grating Base Stamp from Happy Seppuku (odd name) that I received for Christmas. I used green stuff on the bases and then pressed the stamp into the base. I found the green stuff a little tough to work with, and it was challenging for me to get an even surface, so some of my initial tries are a little warped.

Anyway they are now ready to run around my space hulk and get all feral on some poor salvage crew.
The next batch are smaller 25mm bases and I used some old milliput I found in the back of my workbench. I found the milliput a bit easier to work with. One of the tricks is to figure out how much pressure to use when pressing the base into the stamp. Too little pressure and I didn't get a clear impression. Too much pressure and it was very deep and "wobbly".
After letting the bases dry, I trimmed off the excess milliput and here are the results.

Any suggestions on getting clear, crisp impressions are always welcome!