mr surfacer 500

it is harder to sand than squadron but imo gives a better finish.. i always found squadron to "bitty" and soft and couldnt get a nice finish . my current favourites for seam/hole/ejector marks are

3M Acryl-red glazing putty 

mister disolved putty

mister surfacer (500 and 1200)

Use a q-tip and Mr. Color thinner to rub it down. I only sand the stuff on fuselage seams that are easy to get to with a sanding stick. All difficult areas like wing roots get the q-tip.

cool!! thanks for the tip HK .

also iso-alcohol works too

Not sure about Mr. Surfacer or squadron. I fill seams with Tamiya putty, then use a Q-tip soaked with Acetone (fingernail polish remover) to smooth it out. Sometimes I get away with very little sanding.