In ON4UN's Low Band Dxing I found interesting the phased vertical section.
Since you have oak trees that tall and spaced that far apart you might consider
phasing a couple of verticals depending on what directions you could favor with
your tree placements. Phased vertical spacing should not be considered as
discrete distances for placement of the verticals (1/4, 1/2 lambda etc.) but
rather as a continuum. The chart found in the book shows the various patterns
which can be achieved with spacing even as close as 1/8 lambda! A couple
years ago at my former QTH I had erected 3 full sized 80 meter verticals spaced
1/8 lambda over an extensive laid on the ground & buried in the yard - ground
plane. I used lengths of coax phasing line with coax switches modified to
eliminate the grounded when not used; to NOT grounded when not used and
switched lag into one or two of the three elements to give gain and front to
back. Since your trees are so tall this might accommodate 160 with loaded
element(s), 80 meter full sized, and 40 meter vertical dipoles fed half way up
the wires. Another option is a large vertical loop fed with balanced wire and
use your tuner. At the QTH where I had so many tall trees I found myself
looking at several antenna texts, ARRL, ON4UN, and some older references I
have. You will arrive at the option best for you looking at all the options.
Good luck with your mighty oaks!