Domicile and mailing address are two different things — or can be. For example, my domicile is in Douglas AZ, down on the border, but my mailing address is a mail forwarder in Quartzsite.
I have a friend living in Douglas who let me use his address for domicile purposes. I went online and got a blank lease agreement form, filled it out with the friend's info and presented it to the DMV along with my SD drivers license and passport. I didn't need Real ID since I have a passport. Then, a few weeks later, when I was in Quartzsite, I moved my mail forwarding from SD to BCM Mail & Ship. You get two addresses with them: one for mail, one for FedEx/UPS and such. I get very little mail -- two or three pieces a month -- which I usually just have them shred.
I'm not sure, but I think the 7 months thing only applies when you want to claim benefits, like MedicAid and in-state tuition. Otherwise, they're more than happy to take your registration and DL fee money anytime.