I agree with everyone's suggestion for a battery bank as a solution. I've been an exceptionally pleased customer of the Anker products for almost ten years. Well made, great performance.
I see you have the Hondaline Backrest? I use the same SAE cable I use for my Battery Tender to power a compact SAE USB power port, which stays under the seat. I then run the USB cable between the seatbase and tailsection into the pouch behind the backrest to charge my phone and other devices while on a ride.
LightningFast SAE To USB Adapter Motorcycle - Quick Disconnect Plug - Quick Charge 3.0 - Dual USB Ports To Charge 2 Devices
This one has two ports - one of them Quick Charge 3.0 plus the other is 2.4A. It has its own power switch (it does draw power when not in use if connected directly to the battery). Not a problem if connected to a switched SAE connection. Also extremely easy to just unplug from the SAE cable. Mixed reviews on Amazon. I've had two in constant use for the past two years with no issues.
I know the pouch is not waterproof, but a 1qt or 2qt ziplock bag should protect your gear pretty well. You're going to need a means of charging your battery bank anyway.