Originally Posted by AviatorJ
I had issues with that approach. Ended up having to manually build everything up later and then sand it all down. Ended up turning out great but my initial cutting to the scribe line probably made the entire thing much harder.
What I describe is one approach to "building it up later." In my case, sanding the cabin top to a distance of 1/4" away from the inside of the doors was beyond any scribe lines I could make out.
He will have to sand some doorway material away just to get clearance for the door pieces to seat flush for initial assembly (drilling and clecoing to the outside of the cabin while the door bond cures). From there it's very straightforward to scribe the 1/4" gap line from the inner door face, and check progress as he goes with a go/no-go feeler gauge.
In my case, much of the doorway was left with a knife-edge after this final trim. What was still full thickness was checked with a 1/4" gap gauge and if necessary ground down to 1/4" thickness for the edge seal to grip to. The rest was built up with flox, cast-in-place with seal material as the female mold. I'm very happy with the results so far.