virtuemart 2 product linked eachother

project budget max $50 higher bids will be ignored. I have virtuemart over joomla i am preparing air-condition selling site over virtuemart all aircons comes with seperate 2 box indoor unit and outdoor unit the shipping module i use calculate exact amount customer will pay if you write dimensions and kg. However there is only 1 place where you write dimensions i entered indoor unit dimensions but i need to find a way create a product for outdoor unit with 0 dollar attached indoor unit which is 920 dollar what i want you do is 1) find a way when customer hit "add to cart" button it will automatically add 2 products together to cart one of them for (indoor unit original product) the other of them could be child product (outside unit) i tried but didn't success so when customer come shipment information it will calculate 2 seperate box 1 indoor 1 outdoor because i would fill dimension separately for indoor and outdoor unit 2) If you use another product attached to original product when customer try to remove outdoor unit from the cart then it should remove also indoor unit too otherwise customer would remove only outdoor unit and able to continue without outdoor unit to check out process so calculation will not accurate