Re: "There are over 200 roads that cross the border."
But the point is that there aren't external EU/Schengen border crossings without customs posts. Take a look at a map - you won't find thousands of crossings.
I can't get the actual total number, but click though the individual borders listed here. I was very surprised to see how few border crossings there are for each EU/Non EU country interface.
For instance, on the 535km Poland Ukraine border (comparable in length to the Irish one, and describe as "the most often crossed eastern border of the EU") there's a grand total of 7 road crossings (11 crossings in total including rail).
Taking the example of the longest border in the Schengen Area, the Sweden/Norway border (1,630km) has 10 road crossings with customs stations, and only a further 30 with none.