Yes, I've always thought it was an interesting issue to try to imagine the choreography of that long day. The shot from the trailer is helpful in this. I really wonder why that hit the cutting room floor for the actual movie. If it made it into the trailer, cutting it must have been a pretty last-minute decision.
I can imagine that their interactions would be pretty awkward that whole evening. But, we do know that Ennis changes clothes at some point that day. Undressing and changing clothes in front of Jack would have taken on a much different significance of course by this point. He seemed very much at ease changing and bathing in front of Jack earlier in the film (before he was aware of the extent of Jack's attraction), I wonder how shy he would have felt changing in front of him now that all the cards are on the table, so to speak.
In another thread about the whole shirt issue, I noticed that during the first tent scene Ennis is wearing his shirt with the broad brown and blue intersecting lines. It's hard to notice because of the coat... but there are a few moments when you can tell. When we see Jack doing laundry it looks like he's in the midst of washing Ennis's shirt that ends up being the shirt, one of the pair that Ennis discovers at the end. By the time we see Ennis sitting in front of the campfire before the second tent scene, he's clearly changed into that shirt.
By the way, I'm increasingly loving the abrupt cut from the "I ain't no queer... me neither" conversation to the second tent scene. It's like Lee is immediately undercutting those statements or is immediately exposing them as a form of posturing.