Before painting everything, I assembled the model by parts (arms, legs, body, weapons...), except for the clear parts... I applied primer to the model, to see any seamlines, cavities (from cutting parts off the sprue...) and such surface imperfections.
Then applied Mr. Surfacer 500 to any of those imperfect areas... dried, then sanded off the excess with a light 600, then a 1000 grit...
These are just the few of the "fixed" parts... I must learn to practice removing parts off the sprue more efficiently as to not produce any "gate cavities"
I then applied a second coat of primer to the model before painting... This final layer of primer would act as a "sheild" coating against anything applied over it prior to the "gloss coating" after the basic paints, decals, shades, tints, etc...
This method is my SOP for any Bandai model kit since their plastic material has a high tendency to break with using heavy Enamels and Lacquer based paints... other plastic kit brands have been better just enough to hold itself after heavy Enamel and Lacquers and other bases applied...
but I still make it a point to apply primer to any kit, any brand, scratchbuilt or not...
( personal experiences )