Hello! Congrats on your new purchase and welcome to the site.
I just installed an RVLOCK on my rig last week and wonder why this isn't standard equipment of even an option. Personally, I wouldn't worry about trying to match keys because between the keypad and the included fob, you'll never use the key again.
As far as batteries, you're probably are referring to Lithium Iron Phosphate (LiFePO4) not Lithium Ion. This is covered quite extensively in the ELECTRICAL | CHARGING, SOLAR AND ELECTRONICS forum.
https://www.winnieowners.com/forums/f260/
I recently performed this and in a nutshell, there are no panels to open. You'll actually need to drill a hole through the floor in the pass-thru and re-route. When finished, I used spray foam in a can to fill in the void to keep critters out. As a bonus, I utilized the space on the tongue to relocate the spare tire and add a toolbox.
https://www.winnieowners.com/forums/...ue-360779.html
Good luck!