Tarp Techniques

"Barring that, is it easy to set up an 8×10 flat tarp with 3 sides penned to the ground?"

Sure!

1. lay 8×10 tarp down flat and stake down along one side of 10' edge

2. go to the other 10' side that is not staked down and raise the center with a trekking pole or branch, tie off tarp at the high end of pole/branch/tree and secure by staking out line supporting the trekking pole or tying off line to tree, rock or fixed object.

3. At this point you should have a triangular shape formed with your tarp. High end point being raised with longer
10' back section staked out low.

4. Tie off the front two sections dangling near front opening with guylines and stake out to form two front "walls" on either side of the raised entrance

5. providing your tarp has center tie outs or fabric loops secure line around fabric loop (about 10' of line or cordage needed) and pull away from the back flat section and tie off to another trekking pole, branch or fixed object about 2' off the ground and then stake out.

You should now have a pretty stable shelter for two plus gear with 3 sides protected from the elements and one opening in the front.

Read this carefully and practice pitches before attempting in the backcountry

Good luck & hope this helps
Jim