Ok, I think I remember, now.
I used the 2x6 on the bottom against the bottom of the RV floor, supporting a piece of plywood up against the bottom of the tub floor. The white stuff is glue to try to glue the 2x6 to the plywood.
Then, once I was happy with the placement of these two pieces in the hole, I used 2 wood screws with washers to hold the 2x6 in place on the RV floor.
See if these three photos show it better for you. 1610 shows the "whole" picture, 1611 and 1612 show the ends.
I believe I wanted to provide a little wider support for the tub floor with the plywood, thinking the 2x6 was narrower than the plywood. That is the only real reason for the way I stacked it, as far as I can remember.
Get back to me if you need more clarification.
This area is pretty tight to work in and get to. Don't screw your neck up trying to get to it. I'll come down and give you a hand if you want me to.
2016 Thor Hurricane 29M