Thanks, piscean
Waiting for the weekend to try ...
I think the length (ie. ultra tight fitting) of the boards is what bugs us the most ATM. We find that every corner wall - even though it looks totally OK - has a few mm of distortion (or some deviation from vertical) somewhere at the bottom. This distortion prevents the corner of the first board to sit tight up against the wall, so the board that comes next cannot fit, it's longer by some 2 mm plus/minus