Ask Google he knows
I don't believe there's a special software for that. You can use Photoshop or Corel. I'm not experienced in making tarpaulins so I can advise you on dimensions and other technical stuff but I believe that's not that much of a problem is you're experienced in Photoshop or Corel or any other graphic tool.
I mean you probably already know dimension you're working with. The think you have to worry about is how many colors you can use. You have to know who's going to print it cos you have to know what colors they use.
If you're going to design really big tarpaulins you have to be aware of it's resolution. If there's only going to be some simple graphics and text you should use vector images cos they can be scaled to any size without loosing quality. On the other hand, if you're going to use pictures they have to be pretty large.
I believe that making tarpaulin design is nothing special, really. It's just like any other print design.
