Can I get a bsn without an apartment?

I am pretty sure this question has been asked before.

Basically my gf and a friend of ours are already in rotterdam studying for two years, sadly I could not move in at the same time with her as I had to fulfill my military obligations in my country so I had to stay back.

I will move in the Netherlands next month I have some savings to survive the first months. Thing is my gf and our mutual girlfriend are already renting together a small apartment and seeing how it is pretty much impossible for 3 people to rent together in rotterdam im left without many options. I can still live with them but I probably can't register in their apartment

Can someone register without an apartment? I've looked in the rni system but it is only for 4 months, I was thinking to do the rni registration and start looking for a small apartment or rent a room while working with my limited time bsn, what happens when those 4 months pass and I haven't found anything? What are the alternatives.

Im an EU citizen btw with an EU passport.