I recently found a North Face Tadpole 23 2-person tent for $3 at a gear swap, and have been working on repairing its several minor problems. Most of the problems were a series of quarter-sized holes in the floor, which were easily patched with Kenyon K-Tape.
In order to protect the repairs, and help the tent stay dry, I also wanted a ground cloth. Name brand tent footprints are inexplicably super expensive (~$60) and hard to find for old tent models like this one. Instead I took random internet advice and made one myself out of Tyvek, grommets, and glue.
I started by laying out the Tyvek on the floor. I set the tent up on top of it, and marked the locations of each of the poles. I tried my best to pull the poles to their positions when they’re staked down. I then drew a hull around the points, and another line ~3cm in. The idea is to fold the edges in so that the edges of the tarp won’t stick out from the sides of the tent and collect rain water. I used the same corner design as this guy to reinforce the grommet points.
I then cut around the perimeters of the tarp, and applied the glue.
The folds were the most difficult part to get right, and I never quite got the hang of it, but Tyvek is thin enough that it’s pretty forgiving if you end up with a small wrinkle. I also had to go through with one more glue pass after everything was folded to make sure the edges stay glued down.
In the end, all the repairs cost $33.68. I actually happened to already have some grommets, so including the initial ($3) cost of the tent I’m only out a grand total of $27.37, and about an hour of my time.