The short answer is if you are a Cali resident and are registering in Montana to avoid Cali taxes it is not legal. Especially if you use RV in Cali.
However if you register in Montana and stay away from Cali I think you are technically OK.
19'Duramax w/hips, 2022 Alliance Paradigm 390MP >BD3,r,22" Blackstone
r,RV760 w/BC20,Glow Steps, Enduraplas25,Pedego
BakFlip,RVLock,Prog.50A surge ,Hughes autoformer
Porta Bote 8.0 Nissan, Sailun S637