Smile - I did this too! "As long as I needed to" this time, since it just felt like what I wanted/needed.... and I have some hindsight as to maybe why.
-I have lots of Home triggers; most abuse was at home, little in a vehicle. So, safe!
-Also, it's a place where all my inside people focused on life's basics; no-one felt trumped by another's wants/needs as they were the needs of the body and no extras (decor, etc), and we lived entirely in the moment (no fridge) which also helped as inside people were about to/being discovered. I had yet to see a trauma therapist for did/mpd.
-The vehicle reminded us of our body "vehicle"; and as such, was the closest thing to inside-outside "matching". For some reason, the truth of the inside matching the outside was helpful in finding what was honest and real about what was going on with us. (Abuse was very covert and made our head confused, so this was a welcome honesty.)
I enjoyed it. We (one body, many felt insiders) hung out, alone mostly, journalling or talking to our selves... and yes, in our car. Much like a human hangs out in their body (obviously), but as a dissociative being, we never really had. It gave us a tangible way to see what living in our body (or in this case, a vehicle body) would feel like. First time I ever really felt "normal" like everyone else; contained, one moving being with all the parts contained within it.
I took it day by day. It ended up being 3 months. (we'd done it before, but never this consciously). I think I solved something, and don't feel a need to go back. Now I'm working through similar re-structuring of inside people (and new triggers) by being in a home. Lots of work. Quite rewarding though. I'm different because of it!