You have a number of choices on how to setup the controller.
A typical control method (full size vehicles like bulldozers) use two sticks, one for each wheel. If your RC transmitter box has two joy sticks then this would be easy.
Another method with RC is to mix to left/right and up/down of a two axis joy stick. For instance, if the joy stick stays centered left/right then the forward/back movement controls the speed of both motors. If the joy stick is move to either side then one motor turns faster/slower than the other.
Check with RC stores for servo pulse mixing modules and study what they do.