We've full-timed for 16 years and do not receive any junk mail. Way back when, we registered with this site:
No More Junk MailIt helped greatly. Then we had to do our part to keep ourselves off mailing lists. Whenever we ordered through catalogs or subscribed to magazines (no Amazon or apps at the time) we made sure to request that we not be put on any mailing lists. Within a couple months we got very little. What we did get usually had a phone number and I'd call and ask them to remove us from their list.
It takes a little time but it has worked.
We do use the Escapees RV Club mail forwarding service. We use the basic plan but I believe they have another plan to take care of junk mail. Good luck!