Probably a little late, but I tried the Zinc Phosphate. Neither here nor there, wasn't hugely impressed, but wasn't anything wrong with it either. My plane has different primer at every stage. Tail is hardware store rattle can for mating surfaces. Can't remember the brand. Wing I started with Zinc Chromate, toxicity scared me, so tried Zinc Phosphate and then Zinc Oxide. The zinc based primers didn't seem terribly tough, and scratched easily. Fuselage is getting epoxy primer.
So far, epoxy primer is the toughest and my favourite. I started the kit 10 years ago, stored in cool dry areas during the hiatus. The tail looks like it did the day I worked on it. 10 years with mating surfaces only, and not even a change to the shiny. Maybe all the effort and money with fancy primer is a waste of time. Suppose I'll find out eventually.
FWIW, I bought the fancy epoxy primer from the mechanics at work. They alumiprep and alodine everything before epoxy priming. I suppose it's the belt, suspenders and duct tape approach. Those planes get soaked in rain storms, fly though nasty weather, doused in de-ice fluid, land on soggy runways. When the hangar is full, sit outside all day in thunderstorms. Jonny Q. Public tracks mud, snow and grime that settles in the belly. Last week a passenger peed on the floor. A much harsher environment than (hopefully) most RVs see.
Empennage Passed Pre-close Inspection
Wings mostly done
Dash 8 day job is financing the RV8
Donation till September 2021