Single tarp is 2ft too short.

I usually measure the load first before unrolling the tarps. I know the tarp is 25x26. I know with a steel load 21 feet long and three layers high, I can get away with one tarp. The back end of the tarp will reach the deck and the flap will line up perfectly in front.

 

I will measure the load before I even start pulling tarps out. The company issues 8’ drop lumber tarps but I also carry my own 16x16 and 16x32 that I try to use when ever possible.

You don’t have to actually measure. Just count stake pockets. They are usually spaced on 2 foot centers.

 

It depends on what it is. Most of the time you really need to protect the wrapping on the cargo so it doesn't get tattered from the wind or in some cases they have SKU tags that could get blown away.

The tail end or the bottom near the deck of the load is safer to leave uncovered.