Alternate unit of measure

Dear Gurus,

Pls. advise for the following senario.

Base unit of measure of my material is KG.

Selling unit is CAR (Carton).

1 carton is equal to 25kg, so same i maintain in the material master in alternate unit of measure in "Additional Data" tab page.

1kg = i kg

i car = 25kg

plus on gross and net weight i maintain the weight of the product that is 25kg.

when i create sales order system show me the weigh of 625kg if the order quantity is 1 car.

If i remove the gross and net weight than at order gross and net weight field is blank.

and if in alternate i maintain 1 car = 1 kg with out removing gross nad net weight, than system shows me 25kg in the weight if i order 1 carton, but principally that is not correct, bacasue at order in the upper screen shows me the concversion as well.

Looking for the response, so that i can maintain gross and net weight and sell the product in carton.

Hope scenario is clear.

Regards,