Help Needed for sorting out my shipping

Hi,

On my cart at hudsonpaint.net (not yet live) I have set up my shipping rates using weight based shipping but was wondering if someone can point me in the right direction with the following or maybe there is a better way of doing this using another shipping module. I have added the following weight/cost into this module (7:8.00) but if someone wants to buy from us they can only select the below amounts as per our couriers instructions over here in NZ.

4 x 1 litres of paint = 6.59 kg (each paint tin weighs 1.64 kg)
8 x 500ml of paint = 6.59 kg (each paint tin weighs 0.82375 kg)
2 x colored shapes = (These go by size not weight so I made them also 6.59 kg for 2 items so that anyone buying can't select anymore that 2....is this a good way of doing it!!!!)

So if someone selects more products over a weight over 7 kg they get an error saying "Error: No Shipping options are available. Please contact us for assistance!"

After they have contacted us is there anyway they can either add manually the cost of shipping we have given them or is there a better shipping module that the weight based one?

Cheers

Ali

Any reason you can't do:

6.6:8.00, 13.2:16.00, 19.8:24.00, etc.

Then when you get an order of 8 x 1 liters of paint, you either ship them in two shipments, or (if it will cost you less) you ship them in one shipment and keep the difference as profit.