Edited to precede with: The 13' Boler/clones get their standing height in the middle section by dropping the floor down into the frame rails. So there is a dropped floor that is about 4' square. In the back, the floor under the dinette is back up on top of the frame. It's also that way along the sides (except by the door), and across the front.
Partway through the Boler
run, they began making another section f dropped floor, in the center of the front gaucho. This was made for a "slide in" Porta Potti stowage locker. I think the notch came in around 1975 on the Bolers. My 1974 has a thick frame piece that goes across and no notch. All of the Scamps seem to have the notch.
It would be quicker/easier to put a dinette in one with a notch. OTOH, one "consolation" of a non-notched dinette is that the table will be up at window height, for easier looking outside while seated. If I make a dinette, I will probably remove the settee base (to save for re-conversion) and build the seat boxes on top of the (non-notched) platform.
Here is a photo of a Boler
frame without cutout (a rusty one that someone was replacing):
So everything that you see inside that large "square" is the dropped floor section on all 13' Boler/clones. The additional "notch" would be in the form of a chunk taken out of the center of the thick rail to the right in the photo, to add another little bit of dropped floor.
I have a photo of a Scamp
frame saved on another computer; basically, that forward thick frame rail that goes across is very thin in the middle, and a "box" extends forward in the middle (about two feet square). I guess that cross member must not be structural.