ADM and the airport are on the east side of town.
The south side has "downtown" stuff, and the southwest side has the college.
Just north of the college, the west side of Decatur is pretty much the ghetto. Call the local PD to get an idea of the "zone" that you should stay out of. It's a pretty big area.
Forsyth is on the north side, and it's a pretty nice area. Also has the mall and some restaurants.
I agree that there's not much to "do" in Decatur. Champaign has a LOT more to offer because it's a bigger city and the college complex in Urbana helps with their sprawl. Springfield has a few restaurants, an indoor gun range, Scheels, Gander Mountain, and some Lincoln touristy stuff.
If your travel trailer is a work trailer and you're staying in a hotel, look for one of the hotels in Forsyth (right off I-72 at Rt 51). I recommend staying away from the Decatur Conference Center and Hotel. They are working to rehab parts of it, and it has a bar......BUT it's a nasty roach hotel and you run the risk of being up all night with the partiers for the various conferences.