Ok I have finally managed to turn the original .esp into an ESPFE plugin using xEdit which is marked as light but still allows LOOT to sort it correctly - this will work for all versions of Skyrim including SE and VR...

This is a merged version of my Open Sesame - Dungeons Unlocked and Solstheim-Tamriel Rowboat mods combined into a single ESPFE plugin for anyone using both mods. This version does not provide a FOMOD installer and is provided primarily for VR users.