Matt, Bowen Ranch does not take reservations. Keep in mind that camping there is very basic- no facilities. It should not be hard to get any kind of spot if you get to the Ranch at a reasonable time in the morning. Mike the gatekeeper will direct you.
If you prefer not to camp, there are numerous hotels in Hesperial, Apple Vally, and Victorville. A cheap good close hotel that we always stay at is the Motel 6 9757 Cataba Road- right off of Main Street and just a little west of the I-15.