When evaluating LNG tankers or ISO tank containers, the most critical factor is the insulation system. You must ensure the use of high-vacuum multi-layer insulation to minimize the Boil-Off Rate (BOR), typically aiming for less than 0.15% to 0.25% per day. Additionally, verify the material grade; the inner tank must be made of S30408 stainless steel or 9% nickel steel to withstand cryogenic temperatures of -162°C, while the outer shell should be high-quality carbon steel with anti-corrosion coating.