hi richie..just covered up with masking tapes loosely..spray it on the loco body if i were u...when it done...take the masking tapes off....tht wot i do with my kits modelmaking....
( glazed windows, metal wheels, brass bell etc ) TAPE OVER.....ok..
the window is covered with masking tapes...just put it on and cut around the edges or get pieces of scappy papers ,,,measure it and see if fit it..then use the masking tapes on flat clean surface and marked out,cut it and put in on the window..up to u richies...will send u a picture ok....
i never used varished on my locos..mmmmmmm.....coz it acryilla paint..yr is weatherin powder,,so supagav are the expert.......drop him a line....ok?..he will tell u everything...he is so good