> If you truly need to drive for 7 or 8 hours (400-500 miles at 60) without any kind of significant breaks on a regular basis, then I'd argue that you are probably taking quite a risk to your safety (and those around you - both inside and outside your car) due to tiredness.
I've done 350~ mile trips pretty often (about 5 1/2-6 hours) and I usually only stop for 10-15 min to go to the bathroom and fuel up. Driving for a few more hours isn't really that bad, and very common in countries with 10x the square mileage of yours.