We would need to be able to set Invoice visiblity in the Security Group to "view mine" similar to Tickets.

The reason is that when we use technicians outside of our own staff (when they are on vacation or we need rush jobs), we don't want then to see all our tickets/invoices/customers etc. I managed to configure the tickets to work fine with the Security Group editor by creating a new group for extra staff. They can see only tickets assigned to them, but I have to let them see all our Invoices so they can take the customers signature to the Invoice they just created from the ticket.

The Invoice already shows who created the Invoice, so could it be configured in the Security Group as "Invoice - View only mine" checkbox?