Round door mounted would be my call
In another post you mention an emergency solution. A wire in the boot that you touch on battery+The last time mine deadlocked I had to remove the rear window and crawl in but even with the key in the ignition the car would not unlock. Trying to remove the door panels with the doors closed and seats in is a nightmare. You need to gain access to door lock lever that is situated at the back of the door which will involve getting the angle grinder out. Much easier to cut the new grp door skin to gain access to the door lock. Some builders of the 250 left a hole in the skin with a plug to hide it along with an old extended key so the lock could be operated.
It took me over a month to determine the location of my gills. I will post my gill pictures on my forum in 3 hours. I hope this will be a reference for location selection.
Haven't decided where to cut it in yet. Bit higher maybe and a bit further back I think.
I might move it to the door where it'll probably be more useful. On the other hand, the 507 design does look good with mirror on the wing. The foot/base of the mirror I have is very petit though. It needs a bigger base so I might change that mirror one day and get a chunkier one something like @Dxbolton 's. No hurry though. There's a mirror so it's road legal-ishIn my opinion, if the glass were bigger it would hurt the design. How about moving the location?
My triumph herald has small ones on the wings and they work very well.I might move it to the door where it'll probably be more useful. On the other hand, the 507 design does look good with mirror on the wing. The foot/base of the mirror I have is very petit though. It needs a bigger base so I might change that mirror one day and get a chunkier one something like @Dxbolton 's. No hurry though. There's a mirror so it's road legal-ish
For actual "looking behind me" I'm considering side cameras