Transporting mam bottles after sterilising

Hello! After some advice as very confused with mam bottle storage. I’m using the self sterilise method in the microwave, which is great! However, the manual says they remain sterile for 48 hours when left assembled in step 3 (placed loosely together with bottle teat inside, rather than assembled). This is fine when at home as I leave them stored on my kitchen side ready to make up. However, I can’t figure out how you take them anywhere. If we’re out for longer than 4 hours, I’d want to make up a feed once out rather than take pre made bottles with an ice pack. But you can’t leave them in step 3 or they’d just fall apart. Does anyone know how long they stay sterile for once assembled please? Many thanks 😊