I haven't looked at that kit in awhile,however,to fill a gap like that you probably want to use strip plastic (evergreen,plastruc)to fill most of the gap then use your choice of filler. the thing to remember is more plastic, less filler.or strip the chrome off the trim glue it in there then sand and sand or use a dremel until it is all leveled off and smooth shouldn't need much filler after that . hope this helps