I'm not an MD and don't know much about poor leg circulation other than sitting for 12 to 18 hours can't be good. My advice, for what it is worth, add walking to your daily dose of L-Arginine. I believe all drivers can benefit from walking whenever they can. Walking burns calories, increases heart rate, is easy on the joints, improves circulation and probably does a whole bunch of other good stuff! The great thing about walking is you can do it just about anywhere, except in a van or an elevator. It doesn't require any special clothing, just some comfortable shoes. It doesn't even require any special skills or athletic prowess. Even I can do it without falling down. Now if I can just master entering and exiting the rear of my van without scraping my bald head.
I tend to layover at Wallyworlds whenever possible. I've got an app for my phone, Map My Ride, that uses GPS to track my walking route and list mileage. I have found that walking the perimeter of most WalMarts, this includes going all the way behind the store, usually yields at least a ¼ mile. During inclement weather, walk around in the store. For an extra cardiovascular workout, pretend you stuffed a machete down your pants, just to get the floorwalkers to chase you! With my former carrier I got to Des Plaines, Il. frequently. I did a lot of walking in the Woodfield Mall in the southwest corner of I-90 and I-290. Large indoor malls are great for walking. Many have walking clubs that walk the mall before store opening hours. These walkers can give you exact mileage for their inside routes.
I try and walk whenever I can. Park a little further away from the truck stop's front door. Force yourself to walk that few extra feet. If I had more room in my van I would bring my bike.