When I handpainted
signs exclusively I used good latex house paint as a background.
Once I got a plotter I realized that vynull didn't stick to it. I think there is some sort of silicone-ey additive in it. (I always used Glidden gloss)
I switched to using Ronan or 1-Shot as a background.
It dries like glass and vynull sticks to it like sh!t to a blanket.
I hear of people who use Sherwin Williams or Ben Moore latex as a background, and also Rhino paints with vynull lettering. But I myself have not tried those brands.
Maybe try a dry application only when using a latex background, but I still would stick (literally) with oil-based enamels.
Love....Jill