My first house-location question

[redballoon]

I have read and cant find anything about this. I just got my first set of six gourds. I love on the river in Oregon and there is a large space between us and the river that seems to fit the bill in terms of location except for huge standing pines. that would be approx 35 feet from where i would place the house. They are probably 120 feet tall and there are two of them between us and the river that would be off to the side (35 or so feet). However there are no limbs on these trees for at least the first fourty feet and they are sparse. Their girth is probably three feet so it seems like the martins could get in and out freely. Any ideas? thanks for any help