I have done exactly what you describe seveal times.
I dont think this method causes any significant weight penalty because the red and blue trim colors over the white will only take 2 thin coats for good coverage.  Only issue is when you sand down the masking edges of the trim colors before spraying clear you have to be real careful not to sand thru the trim.  To do this I use some kind of a shield and only expose about 1/8" of the trim, use 600 paper wet and very light pressure.  You dont have to take the edge all the way down, just knock off the bulk of it before shooting the clear..

I generally use a white base. Remember that reds and yellow are transparent and will show both variations in the base and the base color. . The solid white base works well for that reason. The white base works well for all colors. Lighter shade blues would also cry for the white base.