Yep, it won't overcharge.
The thing you have remember with multiple panels though is that you lose a lot of efficiency in the connections and wiring. So, four Nomad 20's joined together may only get you 40 watts on a good day. For less money than the four Nomad 20's you could buy one Nomad 100 and have a much more efficient system that should easily peak out higher than 70 watts. The Nomad 100 is pretty darn big unfolded though.
For my weekend trips the one or two Nomad 20's will work just fine and they are a lot easier to set up. If I get to the point that I am able to stretch my camping trips into the 4+ day mark, I will pick up a Nomad 100. If I had a camping trailer of some sort I would definitely go with the Nomad 100.