The printer’s manuscript here reads “on the left of their camp”, but the 1830 compositor mistakenly set “on the left of the camp”. In accord with the reading of 𝓟, the 1908 RLDS edition restored the original their to the RLDS text. The 1981 LDS edition restored the their to the LDS text.
When the text refers to camp(s), the choice between using a possessive premodifier or the definite article the is consistently determined. Basically, we get the for camp only when there is a postmodifying prepositional phrase (there are no instances of plural camps under this type):
the camp of Moroni 4 times
the camp of the Amlicites 3 times
the camp of the Lamanites 3 times
the camp of Amalickiah 1 time
the camp of the Nephites 1 time
Otherwise, we get only a possessive premodifier for camp(s), never the. In the following list, I include the example from Mosiah 22:7:
their camp(s) 10 times
his own camp 1 time
Lehonti’s camp 1 time
Thus the use of “their camp” in the earliest text for Mosiah 22:7 is quite correct.
Summary: Maintain in Mosiah 22:7 the use of the possessive their before camp; not only is this the earliest reading, but it is also supported by other examples of camp(s) in the text.