I am going to self-install a couple of UPVC windows in a wooden-frame shed/garden room - basically a 6x2" stud wall. Everything makes sense mostly, but I am confused what product to use on the woodwork to provide a good seal. I know some sort of flashing is needed at the base but is that just something like Bostik Flashband glued onto the bare timber, and is it only needed on the bottom or all the way round? I'm installing a ply sheath and battens on the wall exterior prior to cladding, so does the flashing go on top or under the battens? I'm in the non-ideal position that windows will be fit after the cladding due to supply lead times so if there is prep-work I want to make sure I do this now while everything is accessible. If I can leave the hole in the wall completely for now, then great.