Oh, great news! (Love the “long” response!)
Getting the bun to move really can work wonders for a gassy bun! The stimulation of trying to avoid the carrier was probably exactly what tipped Dorian’s GI system into working mode – you had done great foundation-work with the meds, the heat source and the massage. It’s great to have some meds at home, esp pain meds. Rabbits are sensitive to gas pain and tend become very unwilling to move when they’re in pain. And that makes the whole gas problem worse.
You said once Dorian was (part) rex according to the shelter, and your description of his fur quality makes it seem likely. My Snöa (mini rex) has ridiculously dense fur, very, very fine hairs that just slip through any brush or comb. Not even the furminator would make much difference on her fur, so manual plucking the loose hair seems the best option for her.
Rabbits that are weaned too early can have sensitive tummies bc their gut microbiota hadn’t had the chance to develop like it should. There are a whole host of microbes in the rabbit gut, primarily different bacteria and yeasts, and their interplay in the gut is enourmously complex. Some types of bacteria seem v important for the integrity of the intestinal mucosa. Rabbits are a lot more dependant on their gut microbiota than humans are, their digestion doesnt rely at all as much on digestive enzymes as ours do. And its not just about the work the live microbes do, rabbits recycle the protein from dead microbes when they eat their cecos. Thats a significant source of amino acids for them, sth like 20-30% of the bun’s daily need. (Buns are wonderfully interesting little creatures in so many ways 🥰)