How to grant record access for Account Team Members without using Territories

Summary:

We have a requirement where any resource added to the Account Team should be able to view/edit all associated records. Currently, we are setup for only Ownership based visibility, and the only way to achieve the goal currently is to add the resource to that Team of the associated records (Opportunity, Lead, Activity).

Is it possible to make custom grants on each object to grant access to the records if they are on the Account Team? On Opportunities, for example, I can only find grants for if they are a member of the opp team or territory, or, if they are a member of an Account Team for Partner Org