I'm using Ortlieb pannier hooks (e162) and rail (e170) for the decaleur, so I can take the bag off easily.

One thing that wasn't obvious to me when I first built a rack for one of these bags is that the rack should tilt forwards, and the tombstone should tilt back. That keeps the bag on the rack even without further restraints. I was using my Acorn bag with just the straps at the brake levers instead of a decaleur. That would have worked, but the velcro that holds the coroplast stiffener in place isn't up to the job, and it would get a bit loose when I hit a bump. I'll post some pictures of the existing rack in a bit.

Things I'm going to change:
A little more fender clearance. I like the rack to be close to the tire, but not too close. I had to modify the rack when I changed bags because the bottom straps pushed the fender into the tire.
Stainless steel mounting points. i was in a hurry and used steel braze ons. Didn't realize they would look quite that bad. Too bad you can't buy stainless rack bosses, I'm going to have to crank up the lathe. I have seen some people use stainless standoffs from McMaster Carr, I might do that for the decaleur clamp.
Tombstone made from 1/4" tubing instead of 5/16" tubing. I like the 5/16" tubing for most of the rack, but it's too big for the tombstone.
ETA: do something about the wiring. Putting it on with clear tape and zip ties just doesn't hack it