We get very little info on trailers, so it is not possible to check drawings for help.
Some general ideas may lead you to finding what is needed, though. It will take a bit of looking at what the actual wiring is on the current setup as there are numerous ways to wire simple things and RV have very little "standard" wiring layouts, unlike houses where there are codes to follow.
This first drawing is one way you might find the two different lights set up to switch off one switch.
The idea is that any circuit has to have a full path to make a "circle" for the power to run . We often say it has to come from battery through any switches and fixtures and back to ground which then completes the circle back to the battery negative side.
This is one way that can be done. Click these snips to get a better view.
When the switch is closed, battery power flows from it to the switch and on to both types of lights and back to ground. Exactly how this will be wired is an open question that will have to be looked over to find where the two sets of lights come together.
One way to seperate them onto different switches is to cut the connection between the two types and add a switch. Cut at the red lines and add the new wires for the second path as the blue shows?
I did not draw any fuse/breaker as the load will be the same as before and no change to the protection is needed.
Simple to plan but it is likely quite a lot more difficult to find where that connection for tying the two together may be found!
I have drawn this as putting the second switch next to the first but if it works out easier, you can pick up the power for the second circuit most any place that you can find 12 volts!