Good looking trailer. Did you repaint the green stripe on the outside or is it just in good condition?
As far as your lights the first thing I would do is try to verify if I lost the ground or the power. Find a way to test a good working fixture so you can reliably identify good power and good ground. Now get a long enough piece of wire and open the first non working light fixture. Connect your long jumper wire between the ground on the non working light and the ground on the working light. If the light now works you know you have a broken ground or bad socket.
If still no light take the jumper wire and try to feed power from the good fixture to the bad fixture. Based on what you find you might be able to pull the good and bad lights off the ceiling and run a wire between them by going up into the ceiling and back down at the other light.
Are you sure that the broken fuse holder isn't the problem for the non working lights?