shipping cost only when certain product in basket

hi,

we're trying to apply a shipping cost to the basket when a certain product is in the basket. i've managed to do this by using the manual shipping method and setting a price of £1. i've then set the minimum weight to 5kg. on the product i wish to apply the shipping to, i've set its weight to 5kg.

at the moment this sort of works as the shipping is added ok but if the user changes the quantities of the product or deletes an item or in any way updates the basket, the shipping cost is removed. i realised that i needed to add 'shipping' as a step on the checkout and this half solved the issue but now whenever a user adds a product to the basket that isn't the one with the shipping attached, i get an error saying:

'The cart items combined weight is too big for all the possible shipping methods'

am i missing something? i'd ultimately just like to attach a shipping cost to a certain product and it stay in the basket when the basket is updated.

many thanks

i've managed to solve this issue by creating another (free) shipping method that applies to the other products that don't qualify for £1 shipping but i do have another question..

is it is it possible to attach a shipping cost to a product?

for example...

if i have 3 products in the basket, one that doesn't charge shipping and two that charge £1, then the total shipping would be £2 rather than £1 for the whole order?

i know i can change an option to 'use price per product' but this adds shipping to everything in the basket rather than just the two products i want to add shipping to.

hope that makes sense!

many thanks