Thanks to EastCoastCB's tip on another thread I picked some catalyst to add to my Valspar (similar to rustoleum but tintable) at Tractor Supply, my first time there, and it worked beautifully.
I went ahead and used the full container to the gallon. It was a little late to start, 5pm, but I enlisted my kids and we went for it.
I ended up painting until 10pm so that I wouldn't waste any. With the outside done I still had about a quart left so I moved inside and used the rest on the interior framing and panels until I ran out. As advertised it went on very smooth and set up well. It needed to because I was getting rain overnight and I needed it done.
This morning I took a look at it and for a first coat it really looks good. It laid down very smooth and the flat area we rollered ended up with just enough of that nice, subtle texture while the rub rails that we brushed on looked smooth as glass.
The pic is hard to judge in the rain and low light but it's not bad at all. It still needs to be a bit darker and browner for our taste but I can definitely live with the really high quality finish as the base coat.