|Most questions are the product of ignorance; that's why you need to ask them. There is nothing wrong with ignorance begetting a question; problems arise only with ignorant answers. So don't belabour yourself, or you may have the admin on your tail for frittering away the world's supply of valuable pixels.
On Towser I cleaned away much of the grey and dirty sealant, scraping it away with a putty knife, then wiping the area clean with paint thinner or Varsol. This makes working in that area less mucky, and the stuff no longer gets on things that are piled too high on the shelves.
By trimming the liner, I think you're likely to make visible some of the areas that the liner was intended to hide, turning a once-in-a-year nuisance into a continual visual annoyance. Also, since the liner is fibreglass, cutting it will make a colossal mess.
I find I can reach all my stanchion nuts with a socket set; there are some however that are best reached with a geared socket wrench (if you haven't seen them, they're just like socket wrenches, but the socket ratchets - very handy).
I'm sorry - I have no idea where to get the edging.
C&C 27 Mk IV