Hi, SSS12!
I can relate to almost everything you've said above about your time not being your own. I just finished my PhD, and writing the dissertation while working in a tenure-track position left me little time to care for my health. By the time I defended, I was 50lbs over any decent weight.
I've done WW before with good results. I was an MA student at the time. I found that as long as I prepared my meals ahead of time (we had a dorm fridge in our office), I was fine. I didn't do field work, though (unless you count foraging the library's stacks as field work, lol), so I don't know if you could prepare your meals ahead of time for that. What kind of field work are you doing (i.e., out in the wilderness or in a more human environment?).
I don't tend to eat a lot of so-called junk food on WW since I really don't seem to crave it. My approach is to eat a mostly ovo-lacto vegetarian diet. For instance, today for lunch I'll be having a black-eyed pea curry that I made in my pressure cooker (an adaptation of a recipe in Lorna Sass's _Great Vegetarian Cooking Under Pressure_.
Good luck with your WW-SB hybrid!