I agree that you cannot plan all your stops in advance - plans & timing changes.
I have had great success with my laptop using Delorme Street Atlas 2007, and their Earthmate LT20 GPS that plugs into the USB. Before traveling, I plot the expected route, call up all rest areas (such as Flying J, or Travel Plazas & WalMarts along the route. I select all as "stop points". The laptop voice warns me of the approach of any; then yells at me & "recalculates" as I cruise on by if it's not time to stop. The wife is actually tolerant of the equipment because it has a huge display that she can see where we are going, & what's ahead. As you approach intersections & interchanges, the display zooms in & lists all the facilities available (gas, food, shopping, etc).
You do not need a wireless connection as all the info is included in the Street Atlas database.
I also recommend joining
http://www.overnightrvparking.com/ Their database for places to stay overnight, including GPS coordinates is HUGE. All the rules & conditions are listed. They may be charging however to join since they have become so large & inclusive. It's worth checking out. Their owner/moderator is detailed to a fault about accuracy. You are allowed to download the database as a member.
Happy travels,