welcome from me & thank you for your reply.
It is correct, to duck and crawling sidewards helps a bit. But with the next attack you stuck again in the rhino. I did this 2 days ago with the rhino near the darketo temple. I was in god mode in singleplayer. As soon as the rhino attacked, I was caught into it. I could not get out, after several tries I could crouch away from it, but as soon as the fight continued I was again stucked in. I could make attacks and all, but as soon as you escape from the rhino, it attacks again and you are stucked. I did this with no helping thrall. I think, when you have a thrall with you, the rhino concentrates its aggro to the thrall, so you have not such massive problems. best to test this is really to attack the boss rhino without a helping thrall in god mode.