You are correct that camping tents are exempt from Mezuzah placement. This is because the Torah writes to place Mezuzot on the doorways of one’s “house.” As strong and well-furnished as your camping tent may be, and though you may live in it for a month at a time with facilities in the area, it does not provide sufficient shelter for people to live in it permanently, and it thus cannot considered a “house.”[1]
[1] Rambam Hilchos Berachos 11:2. This Q & A was compiled by Shmuel Kraines, as heard from the author of Agur B’Ohalecha.