Sorry, I didn't realize that the base was made out of aluminum. I thought it was plastic like the lens. mcgyver is probably right, a snap fit is likely your best option even though it would probably require action in the injection molding tool. If this wasn't an aesthetic assembly, I would...
This looks like a candidate for plastic welding. Does the assembly need to be hermetically sealed (waterproof)? I think you have lots of options here. The method you should choose is dependent on the requirements of the product after it is assembled. Can you provide any more details? I'm happy...
