Philmont Scout Ranch is a BSA High Adventure Base offering an extensive program of treks for Scouts.
Here is how to rig a 12×12 tarp (a method I have heard called the Philmont dining fly tarp) to stand up to strong winds and rain. This rig will keep about eight people (who get along fairly well) out of the rain.
The side guy-line is about 30 feet long and is threaded through the grommets on the tarp and staked down with three stakes. It is passed around the center stake as shown below and finished with tautline hitches on the ends.
The ridge line extends from all the way under the ridge, it is made fast to the poles with clove hitches and leads through the center grommet on the ridge, is looped around a stick, lead back through the grommet and then lead to the other end of the ridge where the process is repeated.
The stick keeps the ridge taut without stressing the grommet; in a strong wind the stick would break before the grommet blew out.
Campmor offers a basic 12×12 tarp of reinforced nylon with waterproof urethane coating. Grommets at all corners and about 3.5 feet apart on the hems. Wt.: 42 oz.