If making a new email address is all it takes to get free stuff then your trial model is broken. If your service stores data, a time-limited trial with no export option is usually enough. If it's more or less stateless, then you need to limit other things as well. Would you be willing to share what the SAAS is? Outside of content providers (streaming, etc.) I've never really seen any reason to abuse trials.

Besides, the whole idea of a "disposable email blacklist" is ridiculous. Are you going to block Gmail? Gmail addresses take like 1 minute to make. If not, you've already lost the battle, so do us all a favor and stop this blacklist nonsense.