Hi,
The best thing to do is call Craola. The staff is quite helpful. I live on the Jersey side and have been to Easton many times. For the life of me, I can't think of a lot where you can park a trailer (except for the SS lot), but I've never really looked either.
Just beware that like any city, the neighborhoods can change fast. Crayola is in a nice area, but the crack heads aren't too far away either (as well as the county jail). This is why I recommend calling Crayola.
While you're in that area, check out the canal boat. If your kids like Crayola, they should like the boat as well.