grab CG Ships and SPUKS Mods..will solve your issues

take off the two back planks and you can place the triangles that are missing then place the planks again just be fast if its not in a shipyard so ya dont sink have everything ready
no mod needed to fill those floors

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2166628261 not a great pic but this was built on official pve before the wipe just gotta think around the collisions hehe decks first in the bow and stern of the ship then add the final planks and no issues at all even tho they clip a little if ya try to build it the other way planks first then the ceiling/floor peices it clips and prevents snapping tho kinda hard to see but theres two angled walls in the bow supporting that foredeck on that schooner also that clip into planks also same thing wood floors and walls first for that section then the final planks afterwards .. basically when i build this style schooner i put in the gunports and ship decks then build all the superstructure above it then add all planks last also prevents gettin stuck in boat till stairs and ramps are up if my grapple breaks lol