No casinos in VA. OP probably heading down I95 and will find no casino in NC, SC, GA or in FL along 95 till he hits S of Ft. Lauderdale. The casino north of Ruther Glen is brand new at the DC/MD border and since they are so space limited such as to begin pay parking, doubt they'll welcome an overnight RVer. Otherwise I like casino lots. Generally with a free casino card, eats are discounted and are available 24 hrs. I park and then call security and tell them where I'm at (well out of the way). If I'm going in to eat, I'll just stop at security and chat.
Big Box stores (that close) are good. Church parking lots are good too if it's not Sat nite and a Sunday morning service church. I do use Cracker Barrels and usually arrive mid afternoon before parking lot fills for dinner. I park in the back cross way across a number or spots that would be last to fill. After the dinner hour, I move to a spot that along a curb/grass and put the slides out over the grass. I orient to ensure an easy out.
In non metro areas and towards evening, I pay attention to those blue "RV Parking" signs that are on the highway. The ones that say "H". The non metro hospitals will not have parking ramps vs. flat lots. Pull in near the emergency room. Security is usually located there and tell security that you're tired and not fit to drive. Ask if they have a corner in the lot where you can park and catch a few hours sleep. Never been turned down. Always offered an OK to stay the night and 'we'll check on you during our rounds'. Most always they'll get in their security car or golf cart and escort me to a good spot. Side benefit is I usually find hospital cafeteria to have pretty decent breakfasts at a value price.
Other spots to look for in decent areas are outer shopping center parking lots but you might get a knock on the door from security now days with shopping centers in the terrorism news. Better might be after hours in a Outlet Mall parking lot.
OP, the Ruther Glen Flying J is a pretty busy fuel stop (lower fuel tax in VA) and would not be on my list of stops. Some more rural FJ's with big lots are OK if you take a far away spot. Bad thing about truck stops is that I wouldn't dare have a slide out.