I don't know how you would place an extra bulb in a LED assembly that does not have room for it.
2019 will have LED assemblies for tail lights.
Get a boat trailer wiring
KIT, it will have all you need to make a wire harness. Run the 4 pin tape thru the Jeep to the tail gate, place a 4 pin plug on that end where you can plug in your extra 2 lights.
I made a small bracket that clips over the top edge of our gate one each side to carry the lights.
Your jeep will not be cut/ altered in any way.
use a 7 pin to 4 pin adaptor on your motorhome,
PLUG and simply plug your jeep harness in to it.
No more fiddling with charge wires, diodes, batteries, bulbs or any thing. just plug and go.
I'll built the harness if you like,,, PM me for phone and e-mail.