Ma'ayan Omer (Maayan Omer 5:1:24) — Ma'ayan Omer (5:1:25) states that there are differing opinions among the poskim regarding whether Eilat should be considered part of Eretz Yisrael or as foreign territory.
Az Nidberu (Az Nidberu 14:43) — Az Nidberu addresses the halakhic status of Elat regarding whether a priest is permitted to travel outside the Land of Israel, noting that while some authorities consider Elat part of territories conquered by the Egyptians (and thus subject to the sanctity of the Land), there is significant rabbinic dispute on the matter, and the work does not definitively rule whether Elat is considered part of Israel for purposes of this prohibition.
Tzitz Eliezer (Tzitz Eliezer 3:23) — Tzitz Eliezer (3:23) addresses whether one must observe a second day of Yom Tov in newly settled areas of Eretz Yisrael, and does not state a position on whether Eilat is part of Israel.
Shevet HaLevi (Shevet HaLevi 5:173) — Shevet HaLevi (5:173) addresses whether residents of Eilat and Ophir may travel to these locations and discusses the halakhic status of dwelling outside the Land of Israel, without stating a definitive position on whether Eilat is part of Israel.