Time for some detail works. I decided to close the plenum cover gap on the passenger side today. You can see in the image below how the gap looks like. I sanded it down to a knife edge (or sort of) and will close this gap with west system epoxy cloth.

Now we need to make sure that the epoxy will only stick  to the plenum cover and not to the diffuser or to the front baffles.
Therefor, I used clear packing tape and some aluminum foil to seal off those parts. Then I used the liquid plastic called "PVA 119" to lay an additional film layer of plastic on the parts where it can't stick.
The plastic is in a liquid form and you brush or spray it on the part. After drying, it becomes hard and forms a very thin layer of plastic.

Used fasteners as it will be in the final installation in order to get the best possible shape.

 Here is how the wrapping looks like on the inside.

Then I layed up 4 layers of epoxy cloth and put some peel ply over it. 

After drying and removing all the masking material, he is how it looked like from the outside.

and the look from the inside. I looks quite good but it will need some filling up on the outside to make it look nicer. and seal it off completely

So the next day I made some flox, masked the front baffle and diffuser again and filled the gap between the new epoxy layup and the plenum cover and front baffle with flox.

 over done it a little so that I had enough material to sand it smooth once it's cured. 

next day it was cured and after a bit of sanding, this is how the final result looks like. 

When I was making the oil door I accidentally drilled into the door. i had also closed those holes and sanded it smooth. oil door looks good again.