be careful with car filler. on tubes especially or if the filler isn't perfect when the tube flexes slightly it can cause the filler to pop open and will leave you with a nice round crack in the paint.
I saw a prime example of this on an old custom beetle (purple to green house of kolor flip paint with a bronze metal flake in it!) the guy did all the prep work himself and everywhere he fill'd had perfect outlines on it where the paint cracked away.
be warned, it may work but there should be a better way.