The details look awesome dude. I don't think you went overboard at all, there's still plenty of open space and a good mix of greeblies, well done.
For barrels I've learned the hard way from doing my
Fuel Rod Cannon that it's infinitely easier to either
cut a channel for
the barrel than adding it after. If you have a foam build having a barrel that runs the length of the prop body to add support, that's a bonus that can't be beat. If you use a harder medium such as wood, cutting out a channel beforehand will save you time and frustration of drilling out and keeping everything aligned. The Fuel Rod Cannon a year down the road is starting to show my mistake with the barrel coming loose and the adhesive mix I poured in to keep everything in place clearly ate away at something inside. This is more a warning for your next build honestly.
For the current build since you can't really split things open, I'd make sure that the barrel is less than half the total width of the prop, drill a pilot hole with a standard drill bit and then work up to a spade bit or hole cutting saw. Make sure you get at least half an inch to an inch deep so that the sidewalls can support the barrel and reduce the chance that it warps out of line over time.