Milliput isn't what I'd choose for filling gaps... I use it to make seat cushions, sandbags, rucks, sculpture arms & legs, and stuff like that... I've also used it for making molds. For filling gaps, I use Testor's white (it can be thinned with alcohol so it doesn't harm anything near canopies) , but most often I use Bondo Red glazing putty. I get it at auto parts stores and it's cheaper, ounce for ounce by far than "hobby" brands of putties... It thins with Testor's liquid cement, and dries fast, wet-sands nicely, and doesn't need primer-surfacer.