People hate me for this..... but some constructive criticism:
I wouldn't have used a 12V power plug. Won't last long. Plus, not rated for many amps, has a tendency to corrode and it may wiggle loose. Use a 4 pole round trailer plug instead. Should fit in about the same size hole. Plus, that will give you ground, power and two other possible circuits. Right now, you are grounding through the 3pt. Not the best choice.
Don't really care for where you mounted the switch..... I mean, you drilled a hole in the fenders for the power plug, just as well drill a hole and mount the toggle in a better location. Like on the lower dash panel next to a fuse holder.
Booms are a lot high if you are spraying round up. If it's even a little windy, it may drift. Several wide fan nozzles close to the ground is best. Less drift. Maybe you made the boom adjustable. You didn't really give any info....
One more suggestion. You may find that you mixed up more chemical than you need and want to take off the sprayer. Make a set of legs or stands on the bottom that you can just set it down on. That way you can take it off easy, and anywhere you want without needing to set in on something.
Overall, you did a nice job of building it. Painted it nice, and it looks good!
