@Hinterlands I take a torch for focus - shine it on your 'main' tree and let autofocus do its thing. then turn off autofocus. also check your widest portrait lenses, f4 can be pretty darned sharp on them and save you a minute of shivering and trying not to jog the tripod. my better metering is "boost iso to stupid-grainy high, meter centre-frame, run the numbers and drop iso to lose grain" - olde Sony's max 30s shutter without cable release = stopwatching it by eye :(
@Hinterlands if you're sticking to no illumination even outside the exposure, take a small mirror and try to moon-bounce to your camera while it's mounted on a target-tree. the contrast helps with focus nicely. alternatively you're at hyperfocal calculations and pacing - go wide or go far