This appears to be the principle entry airport into Paris, at least for low-cost flights. A shuttle tram connects the 3 terminals. Direct train to Paris Gare du Nord for €8.40. (There is both express and local service, so be sure you get on the express train.) Train takes about 30 minutes, and departs from Terminal 2 and 3. The TGV also stops here.
If I needed a place to secretly camp, I would take the train one stop to the Villepint station, which is in the middle of a big, wild forest park. You can easily and discreetly camp here in darkness only, although the area is exposed during the day. If you stop at Villepint and then continue to Paris, the total fare is nearly the same.
You need to allow plenty of time to depart from CDG. The main bottleneck is passport control, which took me about a 45 minute wait on a low-traffic day. (Check-in for international flights closes one hour before flight time, but even that might not be enough time for you to get to the gate.)