The answer is pretty simple, and you are on the right track but you don't need the extra dates table.
Go to your "Project - Data Entry" Layout
Change the portal to come from your "Project_Equipment_JoinTable" table (rather than the equipment table). Don't change the table that the fields come from, leave them all as equipment::xxxx
Just change the date field to "Project_Equipment_JoinTable::Date"
and it all works fine.