Mark, if I'm not mistaken, the walls of your camper are constructed of Styrofoam sandwiched between aluminum panels. The bottom trim appears to be about even with the inside floor surface. So it is entirely possible the seam along the lower outside panel may be leaking.
You may be able to seal the leak with a good clear silicone caulk but the damage is done. The particleboard underneath the floor will continue to deteriorate as moisture beneath the floor has no means of escaping because of the metal sheeting covering the bottom of the RV.
I hope this info helps you solve the problem.