You won't hurt your vehicle, and if you drive like the big rigs you won't be much of a hinderance. For the last three years I've driven from the coast to Greenbank, WV (where the observatory is) every summer, and I can do most of it without being on the interstate. In general I try to avoid Interstate travel as much as possible and take the old highways when available. With your route it's hard to avoid the Interstate without a lot of extra driving, but the secondary roads through WV take you through really beautiful (and steep!) country. Those roads by their nature limit your speed to a more acceptable pace through the mountains, and let you see so much more than what is available along the sanitized Interstate route. All bets are off in winter though as many roads can be difficult with snow. I'd break the trip up, camp some place nice/stay in a cabin, take the slower more circuitous route where possible; enjoy the ride.