How I built a perfect fortress!
Here White played Rb1 and offered a draw, knowing that the half point wasn't good enough to qualify for the Canadian Correspondence chess final. That's already a huge hint. My black fortress holds!
Sacrificing the rook on h6 also leads to a draw; and pushing c5 is risky because it turns the black b7 pawn into a passed pawn.
The black rook stays on the e-file and keeps the white rook away the eighth rank by dropping to e8.
Do you see how chess sometimes surprises you?