I can't tell you about storing foods for special diets, but I can share what a challenge it is to find long-term food storage solutions that do not contain soy. I struggle to ensure enough protein for me and my family without the ability to eat Textured Vegetable Protein, since it's made of soy beans, and I and my daughter are both allergic.
Right now, with regular medication, our reactions to the soy bean oil that exists in just about every store-bought product (such as mayo, salad dressing, vegetable shortening, etc.) are held in check. In a SHTF scenario, the meds will eventually run out, so I'm stocking up on organic shortening (no soy bean oil), and looking for products that are soy free.