First let me say I have only seen one love bug
and I can only speak from my experience with Scamps. When a rear floor is rotted all the way around the edges of the dinette floor the complete rear dinette deck needs to be replaced. The floor is what supports your shell in a Scamp
First thing to do as you asked is to support the rear of the shell. On a Scamp
I stand a 2X4 on each frame rail where the rail meets the rear bumper and lean it against the belly band (On the outside of the trailer). Make a mark on each 2X4 on the at the bottom of the belly band. Then look at the spacing between each frame rail and the shell. On a Scamp
there should be about 1/4" space. If the shell is touching the frame add 1/4 inch to the mark on your 2x4 and cut the 2x4's. To raise the shell I put a block on the rear bumper and try to carefully pry up under the spare tire with another 2X4. If you stand your cut 2X4's on your rear bumper and lean them against your belly band and you raise the shell to the proper height the blocks should drop in between frame rails and belly band.
If the 2X4 blocks don't fall
into place raise the shell as much as you can, remark and recut the 2X4 blocks. At least your shell won't wont sag any further. Now you can start to remove the rear floor section.