Nervous about moving into van with girlfriend

Been dating this girl for about two years now, and for the majority of this time I've lived in a car, and she's lived in a van. We usually do weekend trips together, and work weekdays. Occasionally we'll do a 1-2 week trip together in her van.

We've been saving money for the past year now to do a 9 month trip together, where I would move into her van full-time. A year ago it seemed like a great idea, but as it gets closer (plan is to move in in a month,) the more I'm feeling uneasy about it.

I've never lived with a partner before, and I'm wondering how people pull this off. We generally get along well, but there's definitely certain days where I'm happy to be alone. She can get particularly grumpy on her period, and the idea of being stuck in a van with her during intense mood swings is a tough pill to swallow. She also has a big dog that's extremely needy. Couple this with the fact that my own car will be days away (in storage) if something goes wrong in the relationship...

IDK maybe I'm overthinking this. I'm excited for the travel, but not sure about how I'm going to handle being in close quarters with one person and a huge dog, even if I do love them.

Any tips for people moving into a van with their significant other? I'm freaking out about the transition.