Finally getting some time to work on this again. Got all the pieces glued together.
I realized after gluing the barrel pieces together that they weren't properly aligned. I'm pretty sure that big gap between the cooling fins should be on the bottom of the barrel, not the top. Oops! It's glued in too tight, so will continue working on it for now to get some practice in.
I got the gappy pieces Bondo'd together and sanded down and prepped for spraying.
First layer of filler-primer done, will add 1 or 2 more layers before sanding down again, then will start painting.
The misaligned barrel shouldn't be too obvious when completed and definitely some lessons learned for the next one I'm working on.