No, they don't really need seatbelts but if you're really anal, there are dog seats that hold them strapped in. I doubt a lab will be calm enough to stay strapped in to a seat. I would think that work maybe for little dogs. A passenger seat cover and a rear seat cover hammock style like what I have would protect your car a lot from the dog scratching/dirtying it up. If you have a small place, a lab (especially younger) can knock stuff over with his tail and go nuts. If you walk the Lab a lot that will help. But they need a lot of exercise. I assume when you're retired, you'll have lots of time to spend with him.
Actually my rear seat cover/hammock style thing that I got from the pet store is working out really well. I took the dalmation and the bichon to the dog beach yesterday and practically all the dirt/sand is sitting on the cover when we get home and they exit. A few minutes with my cordless Shark vac and it's all gone. The rear seats underneath look stay unscathed as do the rear carpets. Just laying a blanket down doesn't offer near the protection since this hammock thing stays in place.