Have you considered recycled teak wood furniture instead? Wood, being an organic material, is also subject to expansion and contraction due to temperature changes, which I am guessing is a cause for the cracks. Recycled teak is supposed to be already exposed to the elements for a longer period of time, and thus more resistant and 'seasoned'. I came across a brand called d-Bodhi some time ago which does great recycled teak wood furniture.