I like the idea of a peep on a double.
EAW offers a peep sight that installs into the rear base of their QD scope mount system.
It's not easy to have a comb height that is correct for both open and scope sights and a compromise has to be made somewhere.
I got around this problem to some degree on my 400-350 double by mounting the scope as low as possible using a custom base, low height rings, and a compact Leupold which has a small ocular lens housing diameter.
There is just enough room for my thumb to clear the ocular housing when pushing the top lever to break the gun.
The EAW QD system is nice quality and can provide a reliable return to zero but in my opinion the scope ends up too high and they are also a bit on the heavy side.

It is a sad fact, IMO that a scoped double never has the same wondefull feel and ballance of a quality double with open express sights!