Anything you can do to avoid the trees will help. Cut them down, raise the antenna, walk the roof, etc. Rabbit will probably post the pictures that show just how they can affect signal.
The towers are at a bearing of 120degrees magnetic (i.e. what a compass reads). 108 is the true heading (magnetic heading minus localized magnetic declination).
I feel your pain on not wanting to move the antenna if at all possible. Adding 5 feet of mast might help, it is difficult to say without pictures. If you do that, be careful of nearby wires and maybe consider adding guy-wires. Are the trees on your land? Maybe you could mount the antenna in the trees as I did, using them to your advantage instead of decrement? See my thread 'Reception Help in NH' for details. 40-foot man lifts can usually be rented for $200-$300. FWIW, I also spent countless hours working on my reception issues, DW was starting to get tired of it at the end too.
