I used Rustoleum 2X primer. I usually use Rustoleum Filler Primer, including on the Callisto and Ranger you see at the right. It’s worked well for me and helps fill spirals and other small voids. But for the Excel I don’t care about the spirals (they’re pretty tight, this thing’s launching from further away, and I’m just not going to deal with that many linear feet of CWF, okay?), and I thought the 2X might work better on the plastic nose cone.
And yes, that’s the rotisserie I made for 18 mm motor rockets, kludged into service for this 38 mm one. Laugh it up.