Could someone who knows Philadelphia please give me an idea of the difficulty (and expense) of parking a van for a few days in the downtown area. It's 21 feet long and fits in most regular parking spots but is too high to enter enclosed garages. (I'd hoped to find a nearby state park or campground to leave it in, as we did in the Chicago area, but have had no luck.) Thanks for any suggestions.

Two suggestions for you - I'm not sure of their merit:
1) Philadelphia International Airport offers long term (or short term) parking. From the center of the airport there is a train that runs frequently to center city. I believe that it is available 24 hours.
2) The Septa train lines run from the outer edges of the city, thru the center of the city, and back out the oher side. The fares are very reasonable. The Septa stations have parking lots. I don't know about size restrictions. The Septa lines stop around 10PM each night.

Thanks, GBC. . . . I've resolved to stay as far away from airports as possible these days, but might make an exception since your suggestion does seem a practical one, particularly if we opt for a downtown hotel for two or three days. I was hoping the Philly area had a campground near a commuter train line, but apparently not. The PATCO line into New Jersey is a possibility for day trips, though.

. . . topping, just trying once more for any additional suggestions.

Why don't you park it for free at the King of Prussia Mall and take a bus or a taxi into the city?

PS There are many garages in Philly that are open lots.

Thanks, marg . . . The mall idea sounds good, but I feared that such places might enforce bans against parking overnight or for more than a certain period, 24 hours or whatever. I'll try to check it out.