Honestly, it sounds like early access games are not for you. That always sounds condescending when I type it, but I'm genuinely not trying to be. My friend and I have built a massive fortress, and everyday in the back of my head, I know it could all just vanish in snap. But that's the risk we take playing an unfinished game. No early access game can guarantee your save file will remain intact for the entire term of development.
If it's causing you that much anxiety, for real, just wait for it be finished and released as a complete game next year.
That's just my advice, though.