I'm loving your videos! You're right about the Sovereign being an amphibious machine. Good reason why the stock and even aftermarket coils for it all have long coil cables, so you can chest mount and water hunt or such.
We need more people making videos on Youtube and such for the Sovereigns so I'm really happy to see you posting the ones you've done so far and they've been great. I'll get around to doing some more myself soon. I wish your audio was a bit louder on the targets testing the headphones out. Think I'm going to plug a headphone jack splitter into the GT so I can wear headphones and then tape a small ear bud speaker to the mic on my pocket camcorder so I don't have to use the awlful built in speaker on the Sovereign for filming. Every video I've seen (and done myself) makes me cringe when I hear how bad that built in speaker is. Makes the Sovereign sound nothing like it's smooth like butter/rich audio with great tone alerts. Goes from the Sovereign being among the best of machines in audio abilities, to looking like one of the worst. I bet that's turned a bunch of people off to buying a Sovereign if they didn't know any better watching videos of it.
That box looks the perfect size for the GT. Doesn't look too high or too long to make it more bulky than it needs to be. A bit of extra length is great for not putting a stress bend on the coil cable at where it plugs into the control box. When I get that Planno box I'm going to put some foam padding on the bottom and sides to protect the GT from bumps from waves or such, and also to suck up any moisture should it spring a leak. Also plan to pick up one of those tiny battery operated moisture alarms at a home improvement store to throw in there. With that box shaft mounted on my back extension it should just clear the water even when I'm as deep as to the top of my shoulders, so I've got added confidence there's no leak potential.
If you had another coil for a land shaft then no need to swap coils out. I keep the 12x10 on my light weight home made land shaft because I'll never use the 10" Tornado on land again, and I keep the Tornado on the stock shaft as my water rig. Since I won't need to be swapping coils when switching from water to land hunting I'm not going to get the clam shell waterproof cable connector, and plan to just Shoe Goo the coil and headphone cables routing into the Planno box to waterproof them that way. Shoe Goo is thick, dries clear, and stays flexible, yet it will peal off fairly easy should I ever need the stock coil or the headphones I commit to the water rig.
Again, keep those awesome videos coming!
PS- At $45 those wireless headphones might be something to try out. No delay with them? And how is the audio and how long does the battery in them last?