You have to get the door and the shell aligned to the frame walkway ears first and glass that in first. (See botton note on blocking up the shell). Don't cut your wood floor until you do this. If you put the floor in first you will not be able to align the door later.
I always leave the bottom tabbing on the shell when cutting the old floor out. I cut the top tabbing off flush with the shell. I make a rough template and use cardboard tabs and hot glue to make a final template for your floor. After cutting the wood I coat the bottom of the floor with resin and let it dry.
Just prior installing the floor put resin on the lower tab upper surface, then put adhesive sealant on the top metal edges surrounding the drop floor area. Then coat the wood edge that mates with the tabbing with resin then drop the floor in place. I then go under the trailer and screw the tabbing tight to the wood with #6 or #8 X 1/2" long self tapping PK screws (duct screws) anywhere there are gaps between the wood and tabbing. On top then brush resin in around the edge of the wood. Once it sets up you can tab the top to the shell. The first trailers I used 2" or 3" seam glass cloth for tabbing. I later switched to cutting strips of matting to form the tabbing it conforms better to the curves.
If you cut off the lower tabbing they make gel resin for upside down work. (good luck with that).
You do not want the shell to touch the frame if you can prevent it. I cut 2x4's slightly longer than the distance from the frame to the bottom of the belly band and force them in place to slightly lift the shell.
the top of the wood floor after it is installed. I have used epoxy garage floor paint
or poarch paint
When glassing the floor & bottom tab make sure the garage floor under the trailer is covered with thick plastic.
Good Luck Eddie