You can just use some hard wood sticks, like pop sickle sticks, to secure the components. I tend to build a small frame along the sides of the fuselage and add a hatch.
One thing, if you can, place the battery in front of the reciever. In a crash, the battery could crush the reciever.
Some people use little eyelets and rubber bands. Or you can just use foam and maybe wire ties to secure the components to the belly. It really depends on what materials you have handy.