I ended up buying one of these to try it out:
The extension mirror straps on with two rubber straps that should go around the back of the Lexus mirror. Unfortunately, that mirror is shaped kind of like a wedge, almost as if it was intentionally designed to prevent a good connection for a mirror extender. It’s really a terrible design if you want to tow something. My conclusion is that I would need to rig up some additional straps to prevent the mirror falling off.
A previous post had suggested a mirror that only clamps to the bottom, but there’s no space for such a clamp on the Lexus because again that is a wedge shaped piece.
Aside from this problem with the mirrors, I am so super satisfied with my GX 550, but if I can’t solve this, I may end up having to get rid of it in the future, simply because of the stupid mirrors, and end up getting some giant F350 or something obscenely big like that. And that would mean needing a second car for city living (I’m a solo widower and have no desire for multiple cars).
If somebody made a telescoping third-party mirror replacement that looked halfway decent, I would totally buy it, but these mirrors have a lot of tech built into them so I doubt that’s going to happen.
I wonder if all of this is completely intentional on the part of Lexus, since the short wheelbase might not be great for towing a large camper, even though the vehicle is capable. But I suspect it is simply lack of attention in some areas.
Oh, another note: the tolerance for having the mirror fold in is super tight, so I don’t think any mirror extender is going to work with having the mirrors fold in. You would need to turn off that feature or damage the mirror or the car. This extension that I tried certainly wouldn’t allow the stock mirror to fold in, and I realize that the tolerance is so tight that I don’t think any mirror extender would allow the mirrors to fold back. Something else that was either lack of attention or absolutely intentional to prevent mirror extenders.