Undeliverable shipment

[tdbnbr]

I asked this a few days ago and am trying again by rewording it in hopes to get some responses to tell me eBay's position in such things.   

I shipped an auctioned item out to the winner's correct address. USPS correctly would not leave the package since there was no 'secure location' at the address. They left the recipient a notice of his door to schedule redelivery. I have emailed the winner twice through eBay to no avail. The tracking number says USPS will return the package to me tomorrow as 'undeliverable'. Obviously at my cost for the return shipment as well as the initial shipping cost. Once i receive it back, i will relist it of course and the right thing to do will be to refund the winner his money. But how do i collect the shipping costs? Both ways? Does eBay help with this? Can i open a case with them? The perfect scenario of course would be to refund his money AFTER i deduct the shipping and relisting costs. There is enough in it to cover that, barely.

So i guess the question is, assuming this thing is getting returned to me (it's been two weeks since i shipped it) how do i get eBay involved to help straighten it out?