1965 Safari taillight housing unit

[LHWalters]

Has anyone replaced the taillight housing unit that should be installed from the inside? if so:
1. did you use pop rivets and not remove the interior skins?
2. if installed from the inside how did you go about salvaging the shower unit?

We want to keep the bathroom shower unit and refurbish it.

Thank you, we are new to this. Put on our new axel today, have all the exterior lights working and wanting to finish up the exterior lighting.

Lisa