ok i will chime in on this one.. pull out the long drawer under the floor. There you can see what you are dealing with. as with mine there is not much there very thin sub floor and styrofoam along with some 1x material.
If it were me i would use brass el brackets and attach through the floor flush with the bottom of the slide out. and then also use 3/4 screws and gently screw to the side of the lower floor section..
I actually have a 3/4 inch plywood floor in mine now covered in vinyl tile. the floor was sagging and getting soft. keep in mind family of 4 here with average use of 40 weekends a year of camping lots of use.
enjoy the 881