You asked for suggestions so here goes!
There's not much to the bottom on a slide out. There wont be any joists or framing, probably just plywood screwed upwards into the walls (that's the usual construction - yours could be different). I would leave the slide on the trailer but extended. Then I would surgically remove the floor, 1 half at a time so the remaining half (front or back) can support the structure. Then I would cover the entire underside with a single piece of 1/8" aluminum plate with flat head screws recessed into plate and securing it to the plywood. This would make the two plywood halves one piece again.
It's also possible the entire floor could be removed and replaced as one piece negating the need for the aluminum.
Just one idea from someone who's done a lot of odd projects like this.
