As someone who knows only the very basics of cryptography - would verifying hashes of a file using SHA-1 and a "weak" hash function like MD5 provide any additional protection over just SHA-1? I.e. how much harder would be it be to create a collision in both SHA-1 and MD5 than in just SHA-1?

My common sense intuition is that it would be a lot harder, but I'm guessing theoretically/mathematically it's only a little bit harder given how easy collisions in MD5 are?