I have been using Clausen's Z-chrome Rust Defender as an all-in-one product. According to the company literature, it is a self-etching, high build, sprayable polyester filler that seals and can be topcoated. I like it when it dries properly, but it has to be sprayed when it's at least 68 degrees and it takes so long to dry. I sprayed some yesterday at 2pm (when it was 77 degrees inside my shop and the outside temperature remained in the 70's until almost dusk) and this morning I can still pick it with my fingernail. I had a similar experience a few days ago, and thinking it would never set up, I stripped all of it off of one piece I had sprayed, then realized the next day it had set up on some other pieces I sprayed from the same batch (so basically it took 2 days to set up completely). The literature says it should be sandable in 30-60 minutes, but I have found it to still be tacky in that time frame.
The bottom line is that, for all of the good things this stuff does, I'm tired of waiting on it. The literature warns not to over- or under-catalyze to try to speed up or slow down curing, and I am very deliberate in measuring the hardener (see my post about the volume of the hardener being mis-labeled). It can go directly over bare metal and filler alike, it is very sandable (after it cures), and it has a built-in guide coat, as it dries in one color and underneath it is a lighter color. I pay about $110 per gallon and that includes the necessary hardener. It can be reduced up to 5% with a urethane reducer, but I only do that when I want to use it to seal an area where I have broken through to the metal while block sanding.
I don't have a spray booth, so I like the fact that this stuff sort of does it all without having to spray two or three different products. Is there an alternative that does these things that is a little more flexible with spraying temperatures and curing times?