Ennis reminds me of "Howard's End", one of whose major themes is the search for a home. After losing his parents, Ennis goes from place to place, first with his sister and brother then with Alma then on his own. He never owns a place, is never more than a temporary tenant, and sometimes not a very welcome one. First his sister then his brother marries, and as he says "No more room for me". The places he lives with Alma are rented and the trailer where he ends up not a permanent home.Then if he goes to live with Alma Jr he's going to be, yet again, in someone else's home.
Then there are the tents on the mountain - refuges, but temporary, the property of someone else. And the forces of nature drive Ennis (and Jack) out of those too.
n some ways this reflects the rootlessness of many people in American history, I think, yet Ennis isn't moving in the sense of moving on, or becoming; he's just clinging on at the margins and not in the process of "becoming" anything other than what he started out as.