Our plan is to transport our backpacks in duffel bags. When we arrive in SJPP we will box up the duffel bags (with a broken down box we'll carry) and mail them to our hotel in Santiago. We arrive in SJPP very late afternoon on Friday, May 25th. Will the post office be open at that time Friday and/or Saturday morning? Anyone have experience mailing a box from SJPP to Santiago? Cost? Easy to do?