What we need are:

• Tac (Blu Tac, UHU Tac, etc...)

• Sticks/Toothpicks (2 small pieces for relatively big surfaces, and 1 for the very small ones)

• Sandpapers

• Adhesive Tape

...almost forgot...we need at least a Corsair too or other kit that has similar intake breakdown. I have three of the Corsairs, and all three has different fitting quality what is really interesting as they are all from Hasegawa...

Firstly I put a "big" amount of Gunze's Surfacer 500 in to the problematic area. It's important as it has not a gap only, it has difference in the level of plastic parts too! We need to remove some plastic to level it right. This is why we just can't use the otherwise good solution can be found in the Tool 'n' Tips section here.

Combine the device as per the image below. Concerning the adhesive tape the stronger is better to keep the sticks tight.

The Tac has a wonderful feature: it can be deformed to any shape, and can be used at almost all surfaces. It's 100% that you accidentally wont sand a section "flat" like you should with a harder stuff. I used it for the larger areas of the intake trunk, and I used the same at the corners, where the intake connects to the nose section. To do so, the only job to do is to "break" the sandpaper a bit along a line to be cornered. It's important that the tac should be still there between the sandpaper's cornered section to keep the shape!  Start sanding, and enjoy the results. It worked fine for me. For very small parts you can superglue some sandpaper to a toothpick and use it. It's important that you should change the sandpaper often, as it's "clogging" fast from the hardened Surfacer! I hope it helps! Happy modeling,  Zoltán "neu" Pócza