Don't ask me how it's possible. But I managed to manouver my Venom thus that when I checked LOS with a laserpen to some Grey Knights I couldn't 'see' a single one from the Venom due to the big fat trees. So we decided I couldn't shoot them based on the TLOS rule.
But... Something is itching at the back of my neck. Did we rule this correctly? I mean, it seems strange to me you can be out of sight behind a bunch of trees.
I mean, you are also allowed to replace (or simply remove temporarily a tree) so models fit nicely in the woods.