you can't use the skimmer rules as dethkoptas have their own rules which are very specific in the Armaggeddon codex. In addition, the dethkoptas are mail order only, not released in stores any more. I've played for a while now and they have not been in stores for more than 4 years. The main reason people convert their own is the model is hard to keep together as its so freaking heavy! This way the main reason i converted mine out of all plastic models.