Hey Chris,
I used to live in Dracut (until 2 years ago) and spent a lot of time in the mud off RTE 113 in East Dracut. In fact, got buried for 3 days there. Also did a bunch off rte 28 in Derry/Londonderry NH. Best trails were north of the White Mountain National Forest on the paper company land. I used the Gazeteer map for my guide. You shouldn't have any problem finding a place to go. Another option is out in Leominster State Park. Hope this helps...
Jon M