Joined: Aug 2010
Posts: 12,728
Likes: 2,105
From: Madison, WI
Bikes: 1961 Ideor, 1966 Perfekt 3 Speed AB Hub, 1994 Bridgestone MB-6, 2006 Airnimal Joey, 2009 Thorn Sherpa, 2013 Thorn Nomad MkII, 2015 VO Pass Hunter, 2017 Lynskey Backroad, 2017 Raleigh Gran Prix, 1980s Bianchi Mixte on a trainer. Others are now gone.
Agree with most above, when I use one, under.
On trips where I do not care about weight, I might bring ground sheet designed for that tent.
On trips where I am trying to minimize weight, I bring a cheap emergency type space blanket to use if will be camping on gravel or thorns or rock, but on those trips I almost always find nice soft grass to set up on so I do not use the space blanket. I bought several of these space blankets on sale for less than $2 (USD), 50 grams each.
This coming summer I plan to camp in thorn country, I expect to bring the regular footprint along even though it adds a lot of weight, I want the extra protection for the floor on this trip.
When I was in my teens or 20s, if I did not have to worry about mosquitoes in cooler weather, I often camped under a tarp instead of a tent. Then I used a better space blanket, one with reinforced fabric in its structure, used as my floor.