Encapsulated Propellent Tank Design

Rocket fuel and oxidizer are usually stored at cryogenic temperatures within the rocket. This creates a huge thermal stress on the tank walls. The boiling temperature of methane is -162 °C, oxygen is -183 °C and hydrogen is -253 °C. I propose embedding the coldest tank inside the less cold one. For example, liquid oxygen tank inside the liquid methane tank. The temperature difference between the boiling points of methane and oxygen is just 21 °C. Therefore, the thermal stress on the inner tank would be much less and it can be made thinner and lighter. Same is true with the hydrogen and oxygen combo which has only 70 °C difference. Additionally, the casing of the methane rocket in the worst case would experience -162 °C to ambient temperature difference compared to -183 °C to ambient with the traditional rocket design. More pronounced difference for the hydrogen rocket; -183 °C to ambient versus -253 °C to ambient temperature difference for the fuel section of the Ariane rocket.