I may be missing something here but it doesn't look/read to me like either of those two had the solid (raised) floor there under the couch. I don't see any reference to frame mods, so it seems like they both already had the "niche" there with a door for the porta potti. That makes the floor under the center of the couch level with the main floor of the trailer in the center without modifying it.
Raya, You're correct. The Scamps have flat floors, no raised area in the front. I was trying to answer April's comment about the solid fiberglass structure.
"I love that mod, but it appears that you have a molded bench with the cut out already there. Did your trailer come that way, or did you make the cut out yourself?"
There's a niche and door right in the middle, not really a cutout, but in both cases all that was replaced by custom built cupboards so now there's separate seating and room for a table. See also Barbara's comment above.