Think something like this, but much slimmer up front at the muzzles --mind you this is a full stocked *three barreled* gun-- I'd go with much less wood up front.

In that your gun is a big DGR a full stocked arrangement would likely be heavy, the gun's going to weigh a bit any way you look at it.
That's why I noted that a light gun in some seven millimeter chambering (with light barrels at that) would be my choice for a full stocked double... and it'd be neat to boot!

Splinter forends are what you see the most. Much of that can be accounted to tradition. I really do think that if you're reaching far forward of a small, slim forend a longer forestock might be something to consider. Doubles with long forends that are full at the tip tend to feel nice in my support hand.
Again, what feels right for you is what's important.

Are you going to get down to Butch's shop any time soon?
He might have some range of forend shapes there for you to handle.

--Tinker