How can I fulfill my 90-day report while traveling in Thailand without a permanent address?

If the hotels you have been staying at have been filing TM30's you have no problem.

Ask your current one for a print out of the tm30 receipt and go to your local immigration office to where you are currently staying.

Be warned many hotels especially under ฿1000 dont bother filing tm30's.

What visa are you on ?

Just don't do it , nothing will happen , easy

Many years ago i got it with screenshot of airbnb booking, i used to use agencies back then

™30 is a bureaucratic NIGHTMARE, it's one of the many ways the government tortures foreigners by doing things 1970s style. But the real question is: why are you getting TM30s? You'll waste a half day of your life and several hundred baht in transport costs. You may even be refused, because you'll have to have documents only the landlord has. Yet the consequences? AFAIK the only thing you need a TM30 for is to get a tourist stamp extension. And that can even be "cheated" by staying 1 night in a hotel and using the TM30 they get for you. Just one night.

You do it where you are at the time. Your Accom should register you. Go to the immigration office located where you are at the time.

You can do it anywhere if you have an TM.30 from that city or province. It can be from a hotel too.

The land owner, the house owner, the landlord, or you as possessor of the property needs to report your address within 24 hours of arrival, if you stay at hotels the manager of the hotel must do it.

Just ask the print out if done on-line, or the receipt when done in person, after your arrival.

When your address is registered in that area, you can visit Immigration to do your 90 day inside Thailand report.