In this case, that is just one factor in many to consider. The combination of issues in this situation are what would prompt the judge to look into the overall Best Interests of the Children.My kids are 10, 7 and 18 months, and I'd STILL live in my Dad's RV before I'd live with him and his wife. And I'd live in my mom's lil pop-up camper before I'd move back into her house, much as I love her.
A friend of mine let her son move out into the RV when he was 16... he's 20 and still there... loves it.
Honestly, I'm not trying to strongly discourage OP, but he's going to have to prove that mom is endangering the kids, or is so unstable as to be damaging to the children - and living in a 'camper' isn't likely to make that happen - not when the US government has deemed living in a camper to be perfectly acceptable long-term housing for disaster victims. KWIM?
A friend of mine has 5 year old twins, and 2 dogs (and no job) and lives in a converted garden shed. A 2 ROOM house - not two bedrooms - 2 ROOMS. It might be 14 x 14 total. It's been deemed 'acceptable housing' on at least 2 occasions (her sister used to live there).
And, I'm sure if you were all 3 living in your Mom's pop-up tent it would have been an even longer, more aggravating custody battle between you & asshat.