Slab I take cold showers. It does not need to be ice cold just cold enough for you to be able to feel the pores of your skin close. Don't get in a hot shower then turn it down or the glass will get "Set" in your pores. You have to use a wash rag with lots of soap on it and only wipe away from your torso with the soapy rag. Rinse with the rag too in the same manner and it will pull out the micro fibers stuck in your pores from the days work. If you already do this please disregard.
As far as unzipping, it's best to do the entire skin in one piece for a pattern. Check your stringers for rot too. Caution must be maintained so that the weight of the wet boat on the trailer does not deflect the hull inward creating a massive hook where the trailer boards are sitting. I always block the aft corners of the boat up to prevent that. Also I block the Keel forward of the boards so the keel has most of the weight. If the rot is really bad and I am concerned the gunnels will sag away from each other I stabilize the gunnels too.
Here is the link to my Champion, it is mothballed here to be completed after the Camper is out.
CHAMPION 171SC Full Restoration
The type of cap you have is the same as my Blazer VL100. That flange extends over the floor to be screwed down. Quick fix you leave a 2in flange in the deck skin so you have something to work back to and just dig out the stuff remaining under the balance of deck. This is not uncommon the manufacturers were notorious for not glassing under the deck before laying it down.