I live in GJ so now the river pretty well. The Gunnison is a nice stretch of water but there are some real challenges getting off the river.
Great hikes up both Dominguez creeks to waterfalls, rock art, and a lot of bighorn sheep. Bangs Canyon is a nice place to explore. There are designated campsites RL but I think you can camp anywhere. There is camping at the mouth of Dominguez but the BLM would rather you not use it. It's been abused plus a lot of people will walk right through camp on the hike up the creek. There's a campsite not far below Bridgeport and there is a nice rock art panel close by. Trains are minimal now that most of the coal mines are closed.
The reality is that the Gunnison is not raft or trailer friendly. I duckie it and a good friend canoes regularly. The put-in at Escalante is fine, everything else is unpleasant at best. I haven't seen the designated ramp at Whitewater recently but you have to haul you boat under the railroad tracks. Same at Bridgeport. I think the best take out option is at the bridge on Hwy 141. You can get a trailer close but it's still not easy. There is no portage around the roller dam and the stretch below that isn't great.
Despite the challenges it's will be a nice trip.
When the river calls, the wise one listen.