Yes, you need an approved Form 5320.20.
You will need an actual address where you and the SBR will be, like your bud's or a range. You will also need the name of the county in which the address is located.
You mail in TWO copies, they mail back one if "they" approve.
I don't have a lot of experience filing 5320.20's but in January it took about a month to receive the approval for the last 5320.20 I sent in.
I'm curious how long they might be taking now since I sent one in a couple of weeks ago for a hog hunt in January.
BTW, if you google "Form 5320.20" NFA Lawyers or another NFA specialist form has the form on line in a "fill out, save and print" format which beats scribbling with a pen. Also, you need to have that approved form with you when you travel to your bud's. Good idea to bring SBR stamp and any suppressor stamps too.
JPK