That's going to be the coolest thing on sand. Hay, what about some sort of fixture that locks in the front of the rail when you drive in? Then you only would need to fix the back of it down for transport. Maybe some sort of hooks welded to the back to easily strap down. Since it's always going to be the same car in there some sort of brackets or something that the front wheels fit into? Especially since you have no way to go from front to back inside when the car is in place.
'03 Freightliner FL112, 295" wheel base, with '03 United Specialties 26' living quarters, single screw, Cat C12 430 h/p 1650 torque, Eaton 10speed , 3.42 rear axle ratio