Need good ground at tail light for rearview camera

[nwhouston]

I am putting in a wireless rearview camera (Garmin BC20) on the top of our TM. The plan is to connect to the running light (green) in the tail light assembly so I can toggle to rear view when on the road. The issue is achieving a quality ground. Per the TM wiring diagram the whole aluminum wall is the ground. Clearly the tail light assembly is making good contact as we do not have flickering lights after almost 9 years of service.
My questions: 1) can I attach my camera ground to one of the two light bulb assemblies (lift the attaching screw, set my wire, and then re tighten the screw), or 2) do I just tap into the aluminum body nearby with a small ground screw with the camera ground securely attached via say an eye ring, or maybe there is a 3)? I have attached a photo from today of my specific tail light assembly.
I appreciate in advance any advice. I tried to get from the back roof down the back torsion arm, under the trailer, then to the front under the trailer, then pull power out on the tongue (we have an electric jack). But I could not figure out how to securely get down the torsion arm. If someone has mastered that step and can share some pix and text I would be willing to revert to that plan.
Thanks for all help. The answer to the question as to the quality of the video image from this camera, I would say enough to miss a piling protecting a gas pump, or a small object right behind the trailer, but not suitable for today's youtube market. I have already hooked it up straight to the TV battery to confirm image, etc.

Larry

[BrucePerens]

What is sufficient for a light might be too noisy for electronics. If you get interference on the picture, try running a wire to the frame and get a solid bond there.