Cookie has given you great advice. Allow me to put a finer point on it as I've done this a number of times.
The coroplast is put on as a single sheet per level (main and drop frame) "before" anything else is done (suspension, gas lines, sewer lines etc.). As such, yea, getting if off in a single piece would likely not be possible.
I think by looking at it very carefully, you might get by with cutting across it in a single place and removing it in 2 pieces for the main floor and then the drop frame section in a single piece.
Whenever removing the coroplast that's been installed with Tek screws and fender washer, always use a small electric impact driver. Using a standard drill will usually snap the Tek screw heads off. It's very rare in the past many years of removing these screws with an impact driver that I've snapped a head.
I use this one.
Have on hand, the following supplies:
- Socket Hex Screws (get a dozen - remove one of yours and buy the same size)
View attachment 59322
- Fender Washers (get a dozen - remove one of yours and buy the same size)
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- Truss Head Screws x 3/4" (get 100 ea)
View attachment 59321
- Scrim Tape (get one roll - share with your friends -
Amazon link)
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- 1"x3"x6' board x 1 ea or maybe 2 ea (I've used pine, poplar and oak)
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If you will be replacing your fiberglass batt, consider using Rock Wool -
link. It's heavier but will not hold water. I've used it in the underbelly before. Buy the special cutting knife for it too.
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I use the boards to use as a splice point for the coroplast where I cut it frame-to-frame. I try to may my cut in a spot that is easy for me to work at on a creeper and not have to fight with axles, frame crossmembers etc. I trim the board to a width that allows me to angle it into place on top of the flange of each I-beam, then I use a Tek screw through the flange (from the bottom) to go up through the flange and into and through the wood. One per side has been effective. You'll want to position this board in the center of where 2 pieces of coroplast will come together.
Once these boards are in place and you have placed your coroplast back and pulled the ends of it to the board, use the truss-head screws to fasten (stitch of sorts) the coroplast to the board. I use about a 3" to 4" spacing. Once you have both pieces of coroplast fastened to the board, you're ready to seal it. Don't worry that you weren't able to completely pull the coroplast back together where the edges meet. I generally run a gap if an 1/8" to a 1/2". Now it's time to use the Scrim Tape. Practice makes perfect with this stuff - trust me. What I like to do is tape the seam with s single section of Scrim Tape. Peel about 1" of the paper backing off the tape. Centering the tape over your gap at one side of the frame, tape down that 1" section of tape over the seam up to the beam flange. Then carefully pull a couple feet of backing off the tape, pull the exposed tape tight and carefully place the tape over the seam. Use your hand to go back over placed tape to firmly press/smooth it into place. Repeat until you get to the other beam, then cut the end of tape at the roll. Done! Don't working of you need to use more than a single long piece of tape. It's a bear to get the backing off and way more time efficient to try to do it in a single piece but not always possible.