why do drivers who drive those artic tri axle tipping trailers go to sleep with the tipper in the air a bit. 
So that if it rains, no water collects in the trailer ? having said that, the quality of sheets nowadays, they should be watertight anyway . . .so bang goes my theory !!
It also stops water collecting in the sheet and possibly ripping it or leaking into the trailer.
Going off the subject slightly , you want to try getting 750 gallons of water off a tilt roof when it has been stood unused 
without puncturing the cover 
Wheel Nut:
you want to try getting 750 gallons of water off a tilt roof when it has been stood unused
easy peasy
Schmidt now has an airbag system to lift roofs so that the water flows off !!!
wizardofoz:
:roll:
Why the rolling eyes?! Like others have said, to keep rainwater off. I’d only ever do it in the winter if there were a chance of frost overnight as the sheets aren’t really designed to be walked on to get the blocks of ice off in the morning, plus i wouldn’t really fancy the idea of walking up there on ice anyway! So long as you have no holes and have two bars across the trailer and one down the middle of the sheet they shouldn’t hold much water anyway.
also depends whats been carried if you’ve had clay or ash something like that if you leave the body up gives the stuff time to slid on to the back so you don’t have to get in and dig it out.
Reminds me of when i used to pick tilts up and could be 20 miles up the M4 and bloody great chunks of ice would be coming off the top and shattering on the road. If any damage was done to following vehicles , would i have been liable ?
Then , who cares it was a long time ago 