Really? You might wanna recheck this sentence, as it makes no sense..................
"They do not have to be stamped "declassified" because Trump can still access them if the are not declassified."
If they are not declassified, no, Trump cannot access them as he is no longer president, and no longer has a need to know. In order to be able to access classified documents, not only do you need the required clearance (and I'm sure Trump's was voided after he left the WH, just like everyone who has a clearance has theirs voided when they leave the billet or job that they needed it for), but you also have to have a need to know.
And, I don't care how "safe" Trump's mansion is, it's still not a place that is allowed to store classified documents.