There's some good suggestions here, but maybe they presume too much.
Putting a tarp over your wood is ok, as long as you're just covering the top, it isn't that different from 'puttin some tin over it' . I'm pretty sure you didn't say you were going to wrap it up air tight like a christmas present with a tarp.
You could spend all the money that Bob suggests on that strapping device, but seeing as it's something you won't often have a need for, surely just a few $5 ratchet straps from Canadian tyre or some place similar would be the more economic choice.
I guess if you're planning to dry lots of lumber yourself, having that strapping device might work out better than just buying the 3 ratchet straps you need for this wood.