As already mentioned there’s a dang good chance the sender is already grounded via the straps and or trunk floor, but I wouldn’t trust it to stay that way myself.
I wouldn't trust it, either. My cars all have rubber strips between the straps and the tank, and the "tarpaper" mat between the tank and the trunk floor.
The better your ground, the more reliable your fuel gauge will be. There's usually a pretty good lip on the corner of the tank pinchweld that you can screw a ground strap from the tank to the body or frame rail if all else fails.
