Well, I love a challenge, so I'll chime in.
dkm365--great freakin' post. Great advice. You really didn't leave much for me. I especially like the cooler/grocery store idea, as that was something I was about to say. Only thing is it might be hell on your joints to run for extended amounts of time at your weight.
I'd suggest working that up slowly. Go till you feel tired, log how long you went, and then try to beat that the next time out. As far as cardio, it might be better to do stuff like farmer's walks with dumbells when you want to take a break from running. It'll work the grip, give your joints a break, and work really well.
Local parks, and at least a couple rest stops I've been to, have a jungle gym type thing and some trails--the jungle gym comes in handy for a lot of different stuff, just use your imagination.
I cannot recommend adjustable dumbells enough (aka Powerblocks)! You can carry them in the back of your cab, and do exercises whenever you have time to stop. I have a hatred of all things bowflex, but I have to admit I've never used their adjustable dumbbells, so I can't speak for them.
My advice is to get the heaviest set of dumbells you can find--it will be a lot easier to spend the extra money in order to give yourself extra room to grow. That way you only have to do it once. If you get a smaller set, then what happens when you out grow them?
You have to spend all that money over again for a bigger set. If you're gonna get some adjustable dumbbells, look around and bite the bullet to get some that will allow you plenty of growing room.
Bottom line is you're in a tough position, but you can make the most of it. It'll take a lot of creativity, but with a little thought you can get something done. Lunges, farmers walks, dumbbell squats and deadlifts,floor presses, swiss ball bench press, swiss ball abs and db weighted crunches, curls, overhead presses, dumbbell flyes, dumbbell rows, pullovers, etc. These are just some of the exercises you can do.
You can do just about everything you want. Throw in pushups, body rows (also known as "fatman rows"), and you should be good to go.
Diet--well, you're stuck in a tough spot here, but good on you for kicking the coke/soda habit. Green tea is great. In addition to what dkm365 said, I think you should spend some time when you're at home and prep a bunch of meals you can keep in the cooler, or that can be kept unrefrigerated, and pop them in the truck when you take off.
You may only be able to make about a week's worth of food, but if you keep the cooler stocked with ice it's as good as a fridge--and that's one week less of food you need to worry about.
I'd grab real wheat bread (looks like it was made with a wood chipper ) and sandwich supplies at grocery stores while on the road, but I'd suggest making big batches of chili or pot roast or steaks while at home. Fish and chicken too. That way you don't have to eat sandwiches every day for the first week or so while on the road.
Heck if you've got room for a big enough cooler, you might make it up to two weeks. Fruit keeps well if you keep it iced, and apples/oranges keep pretty well in the open.
Do you have a microwave in the truck? I know some cabs have an outlet for electrical stuff like that, and you could warm up your steaks or roasts there. Or you could run a Foreman grill off the outlet for chicken and other meats. I can eat good chili cold with no problem, but you could heat that up too.
Also, there was an article on fast food emergency strategies you would really find useful--It's called "On the Go Nutrition" by Mike Robertson. Runs through stuff you can use on the road. I should mention that most fast food joints have a decent chicken selection--if you get grilled chicken (not nuggets/wings/breaded chicken).
Tell them to leave the mayonnaise off and ditch the bun when you get it. Add a salad, which most joints should have, and you're good to go. You just have to stave off the temptation to get the "Gut Enlarger Xtra Bacon D-lux Burger Special" with a side of fries. If the temptation is strong, then just avoid the places and stick to subway, grocery stores, and sandwiches.
Finally, check out "It's Not About the Food" by John Berardi--some extremely useful tips on how to manage the food prep at home without cooking all day long. Would also come in handy prepping for your 3 week long trips.
Good luck man--it will be hard, but it's definitely doable if you can bring the determination to the table. That, however, is up to you. We can't really help you with that. The week you're home, check out some gyms and train there for a good change up--do the stuff you weren't able to on the road.