Hi Smougtea!
Thanks again for pinging about this. I released a patch that I hope fixes the issue. I was able to host the game in headless mode, and then join it from a full client. But I couldn't do a proper test without another player and computer in the mix, so please let me know if you try it again and what happens?
FYI - be careful that the mod doesn't upgrade all your turrets at once, it will leave the base vulnerable to a big attack.