There are many posts on iRV2 concerning the various locations of fuse panels in the Winnebago/Itasca diesel coaches. Here is a link
to the result of a Google search for iRV2 posts containing the terms "Freightliner," "fuse" and "location." Here is a link
to the same search with the additional term "trailer."
One or more of these posts should help you find the fuse panel for the tail lights.