Best way to implement excise duties / excise taxes

Dear All,

what would be the best way to implement excise duties in ofbiz ?

An excise is an indirect tax as e.g. VAT.

The main difference between excise duties and VAT are :

1) excise duties are not calculated on the value of the product, but on
the unit.
e.g. for beer in a lot of countries it is calculated on the combination
of the liters your are putting on the market and the strenght of the
beer on the "plato scale".

2) in B2B discounts are calculated on the sales price excl. excise
duties in case you are the company who is paying the excises directly to
the government. For other companies most of the time it is considered
part of the costprice.

I think that there are different problems :

a) defining that a certain product is eligible for excise duties (e.g.
its is a tobacco product, beer, wine, petrol etc)
b) the calculation of the excise duty itself, which is completly
different per country.

    e.g. In France the duty is a combination of degree plato and volume
    alcohol
    In Belgium they have the notion of a small brewery which allows for
    a discount on the excise tariffs
    etc etc

c) defining when the excise duty needs to be applied. (excise duty needs
to be calculated when you bring it on the market leaving an tax free
warehouse, transportation between tax free warehouse is free from excise
duties)
d) defining that certain warehouses are tax free warehouses
e) legal constraints when re. excise duties re. "nomen clatura" used
e.g. specific transportation codes when transporting the excise products
(transport mode code, transport unit code), product packaging codes,
Excise product codes that in turn as based on CN codes (statistical
nomen clatura used in the European Union), etc etc etc

For the last problem I think I will need to create new entities in ofbiz
and import the official "nomen clatura" but what is the best way to
implement the rest without breaking standard functionality of ofbiz.
(don't want to prevent easy upgrading nor existing functionality as e.g.
the promotional engine etc)

Kind regards

Tore