Flipping it on it's end to give it 48" of vertical space would be best. However I think you can give plenty of climbing space with it oriented with the long end being horizontal just fine.
Add plenty of sturdy branches and sticks that run on a diagonal across the tank. I find its best to use branches/sticks that run from end to end of the cage, less chance of them falling inside, especially ran from say, one corner of the cage to opposite corner on other side of the cage, so the stick cuts through center of the cage. Cork bark can be used along the back wall for vertical climbing space (or just let the geckos use the side of the cage for this too). Fake or real plants can be added to provide cover/attraction to cage.
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PHLdyPayne