Lay the straps on the floor, then lay the door on the straps. That way if you don't get enough compression you can tighten it down a little bit.
I would be concerned that you could actually get to much compression and then have a hard time latching it when the straps are off. If you compress the hinge side to much then when the straps are off, the door will want to pop open, making it difficult to get it closed and latched. My point being, I think it might be better to use as little force as possible to get the compression that you are looking for and then weld your hinge and latches on.
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