Dear Daniel
For proposing the increase in Manpower for your warehouse, you must make clear about the what are the development you are planning to implement, How much work load got increased till now and How much is expected to increase and how you have derived i.e., about the purchase of material in last three year and expected to be purchased during next three years and last three years production and next three years production proposed. How your work got increased in multiples and how further it will increase? What are the cost implication, how you are going to convert the cost into revenew?
Based on the above points prepare your own justification, discuss the same with your management and then submit the same to your top management.