It is a beautiful canyon! I've only floated it once and the fishing sucked for us too, but we were on a Bachelor party and had fished the Mo for days before, so the Dearborn float was all about partying.
There are two pieces of state land that the river intersects on the lower (and most popular float). The first is from about 2 to 3 miles below the 287 put in. There is another very small piece just about half way. It is on very sharp 180 degree bend and would include several small camping sites. I haven't overnighted the river so this is based on Montana parcel information. Another option would be to put in at Hwy 200 and float to the state piece 2 miles below 287... that would be roughly 10 miles of floating through all private land to a section of state land that the river flows right through the middle. If I recall correctly it would leave you 17-18 miles to get out our maybe 8-10 to the second piece of public. The second public piece appears to be pretty isolated while the first has several ranch roads traversing it, but there should be plenty of camping sites.
There are several other stretches occasionally floated above but they have even more limited public land. The 434 bridge down to 200 has one piece of state land about 2 miles from the put in. Another put in at the Dearborn Canyon road put in has no public land along it. Note in each of these cases there is no public land at the put in, you are using the highway right of way to access the river and it can be fairly difficult to put in without carrying your rig in piece by piece.
Yesterday's gone on down the river and you can't get it back. - Agustus McCrae