I was having some trouble with these seams towards the front of the fuselage. They are not suppose to be filled, but there are too big of gaps in some areas. I prefer to use testors putty instead of the squadron for things like this, because it's easy to work with and less of a mess to clean up after wards
Note: I noticed that some parts of the fuselage like the hatch, stick out too much. On an actual P-40, the hatch is flush with the fuselage. You will need to sand down these areas on the photographs. some of these details are on both fuselage halves.
I need to get some more filler, drill bits and a scribe, but my hobby store is going to be closed for a few days because there moving into a bigger store!!!
It's too bad about those Seams !!! man, It would test my pentience !!! but with a little glue putty and controled sanding... you will get her to behave...