We just purchased an intex xtr rectangular 12x24 agp. My 2 biggest concerns are getting the ground 100% level and what to put under the legs. Intex says to only use 15x15 pressure treated wood but I cannot find 15in width anywhere. Other people use 4inch thick 16x16 paver. I need suggestions. We live in Wisconsin, also do people leave this type of pool up in horrible winters? I see people with the round straight leg pools do around here, but not sure with this type of pool, especially how in caves in on sides until the pool is full