I have been using just black epoxy primer for all the frame and under-dash parts that call for a gloss to semi-gloss finish. The rattle cans give just a little more gloss. When I rattle can I use it on bare metal and with no additional painting. With the primer, I use it on bare metal with no top-coat for frame parts, and with a color top-coat if I need another color other than black (Unless I specifically need grey or red for a job, I always buy black primer and keep it for small parts). Because the rattle-can paint is very thin, it seems to resist chipping even more than the epoxy paints.
Like in your case with the weather, I often don't want/feel like mixing epoxy primer. The end result is I would say my car frame parts are about 2/3 epoxy primer showing, and the other 1/3 is rattle can.
Oh, I do also keep a can or 2 of Rustoleum on the shelf. If I have a part that needs a little better finish, yet I still don't feel like mixing, then I will use a couple coats of the Rustoleum over bare metal. It covers the tiny sand marks completely with 2 coats, and looks much better than "frame" quality. The cheapo cans would take at least 4-5 coats to completely cover sand marks...so not worth the trouble if you need smooth.