Nachson was made an elder

Yalkut Shimoni, Numbers 7:36.

G-d torches the edges of the camp

Numbers 11:1.

The Midrash explains the extremes of the camp were the 70 elders

Midrash Rabbah ad loc

The connection :

Seder Olam Rabbah states that Nachshon passed away in the second year after Exodus. The Rebbe connects this to the death of the elders (Igrot Kodesh, vol. 3, p. 225).