Sounds like a good plan Russ.
I have one those 3 grain brass plunger primers in my Range Box - however I don't take my Range Box with me to the Range anymore. In fact, the only place I ever take my Range Box is to Rendezvous and keep it in my tent until I need to get it out to clean my muzzle loaders back in camp after the shoots.
For many years now I've found it so much easier to grab my (rifle, shooting bag, and horn) and off to the Range I go... I also take along a little leather bag with, cleaner, oil, patches & brushes, q-tips, and pipe cleaners in it - to give my muzzle loader(s) a quick Range cleaning before heading back home where they get the full cleaning experience... I only live about 1- 1/2 miles from my local Range.
Anyway, I do find the little priming horns handy especially if you have powder horns that aren't very friendly to prime with - such as some that I own.
Have fun with it Russ and enjoy the build. And welcome to the tinkering club!