Are they needed at Trail camp? I've decided to go get the Hogback tent and reviews says it has no ground sheet.
I have no idea about polycryo ground sheets. I've been using a Tyvek sheet for extra floor protection, although I've also gone without for entire Muir Trails and never had a hole poked into a tent floor. The ground at Trail Camp is mostly pretty eroded granite, which should be fine for a night or two without ground sheet. If it gets really wet, it will depend more on your site choice than how much you can stack under your tent floor.