The PJ4/callsign is the norm nowadays. Reason is, this gives the country/entity _first_, rather than second, to identify the location of the operator first. The practice is established by the country from which the operation is taking place, however, and may vary.
Normally, a "portable" station's QSL route would be directly to that station's primary address, but not always. Many contest operations and DXpeditions have specific QSL routes which have nothing to do with their home station address, and many have QSL managers. It is always best to simply ask "QSL HW?" during the course of the contact, and get a reply.
Major operations usually have a website, and many have their entire log posted on the internet so you can look yourself up and assure that you're in their log, prior to wasting postage, IRCs, etc. If you do a search using one of the major search engines such as Google, just type the callsign you're looking for and see if it comes up with a site.
73 de Steve, WB2WIK/6