I made it as follows:
1] Important to start with a FLAT BED to work on. I did this by constructing a frame out of 6" x 2" Timber, and leveled it by using wedges.
2] I screwed and glued 3 layers of 3/4 MDF for the Larger width ( Remember the bank vault :) ) - also take care not to put screws where the door latch and hinge screws go. SO plan in advance.
3] During this part of the construction I routed out and glued hardwood inserts where the hinges are. MDF has a grain, and isn't so strong along the plane where the hinge screws go.
4] Once this structure had dried ( Put some weights on it to keep flat while glue is drying - I used a few bags of building sand - pretty heavy ), I then routed a locating channel around the edges to take a hardwood frame for which the gypsum board would sit inside. The outer edge of the frame was 20mm ( just over 3/4" ) from the edge of the Door. This 20mm is where the 1st half round seal goes.
5] BEFORE constructing the other 2 layers of MDF, I hung the door - it was still heavy but my woman and I lifted it on to two wooden wedges, and it screwed into the heavy frame easily - I used 4 heavy duty hinges. Ball bearing hinges are best.
6] I then screwed the layer of gypsum board inside the hardwood frame area., and then
7] constructed the final 2 layers of 3/4 MDF - same method as 2]. remember this layer is 20mm smaller all way around, for bank vault effect., and once this was dry screwed this to the already hung door.
8] Then I fixed the latch assembly and used contact adhesive to fix the half-round seal (16mm diameter - approx 5/8") With double 'half-round' neoprene seal.
Your door: Your door is 4.375 inches thick. It has mass, thickness, multiple materials, multiple seals. Were you able to get continuous seals? I've only recently found a way to get an air tight seal into a corner.
Yes this was easy. simply miter the seal with a sharp knife at 45 deg I used the same contact adhesive to glue the mitered edges together. Although to be honest the compression would do the trick.
9] I then fixed the door in the close position with the latch, and fitted the jambs (bank vault style )
You have to be careful with warping. The door has warped slightly, but only about 2mm, and if need be once I've finished, I'll shim where the seals don't quite, erm, seal. but it seems ok at the moment. You can easy check by sliding a thin piece of paper between seal and jamb.
I should mention that I put the seals on the door, rather than the jambs. This was to prevent feet wrecking the seals. I also routed in aluminum angle on the two door thresholds, to prevent foot wear and damage.
Like I say I've only fitted one door so far. The studio is a room within a room design, so I have to build the inner room first :) - Next job after the current job of laying the concrete floating floor.
Anyway, pictures paint a thousand words, so I'll upload some pics in a minute so you can see how I've done it. And Eric can see one of the reasons why It's taking me so long to build the damn studio :) :) :) :)