I don't know of a good way to add freight cost to your inventory item.  The costs come from two different vendors, usually, the material supplier and the freight co.  If you keep adding freight cost to your FRTonPO item number, you have the problem of relieving that balance as material is used.  That is more trouble than we want to deal with.
 
We cover the cost of freight by building it in to the standard cost for the finished product.  You add a freight per unit amount for the type R BOM items in the "enter stds" section of IN-B.  Then when the finished good part standard cost is rolled up, the freight is part of it.
 
DBA inventory transactions are costed on the "average cost", so we make sure that the very first transaction for a new FG part number is "enter finished production".  That way the standard cost sets the average.  If we need to ship before we are ready to enter finished production, then we do UT-K-F to set the average to equal the rolled up standard.

DBA (including the International landed cost module) uses the Freight percentage in the inventory to burden items with freight.  It is an approximation that is verified by comparing the balance in the Freight In account and the Absorbed freight in account.