I'd avoid a slow-blo. Even a regular fuse takes far longer to blow than you might expect. The main current-drawing device in these things is the peltier and as far as I know there is no surge current when one starts up. The fan would see a surge at startup but it's a much lower current than the peltier (100mA versus 5A).
Is there no indication on the original fuse about what type it is?
Is there no indication on the original fuse about what type it is?