these are persistent virtual machines? I would have thought that this has already come up here, apparently it hasn't.
Installation on Linux doesn't take long even if it involves Talpa compilation. I'm not sure that there's much advantage when it's already in the image. Haven't found an article that describes how the installation could be reset.
I'd create a package using mkinstpkg and install on the template machine while it is disconnected (similar to the instructions for Mac OS X), then take the image.The OS X article also describes how to reset RMS if necessary by deleting/changing the relevant files, names are magent.private and mrouter.private, path is /opt/sophos-av/RMS/ though. Not sure if /opt/sophos-av/engine/machine_ID.txt can stay.