There really is no absolute right or wrong in this, but some options make it more complicated depending on how you want to QSL. I've posted some of this to the reflector in the past, but here's a quick summary.
1. First of all, you can legally operate as W7RIV. FCC does not require you to use a portable identifier--it's your choice.
2. Second, you operated as W7RIV. That means that you have to QSL as W7RIV. You can't change the callsign you operated under after the fact. But you do have to keep your log entries separate--don't just mix them up with your regular log entries as you want to QSL them from DM49, not your home QTH.
3. If you only want to QSL on paper, it's easy. Just make sure you use "different" QSL cards for this activation. That doesn't mean you have to print new ones--you can hand-write on paper cards your actual location (town, grid, etc). But please make sure the cards indicate where the station really was.
4. It gets more complicated to use electronic QSL systems, and the way they work is different from system to system.
4a. For LoTW, you use your regular W7RIV certificate since that's the callsign you used. But you have to create a new station location, associate that location with the W7RIV callsign certificate, and sign the cards with that combination.
4b. For eQSL, you need to establish a new account for the new location. Accounts are defined by callsign and a contiguous time period, so this new account is defined by W7RIV and your hours of operation. But here's where it gets messy--it means you have to end your current W7RIV account at a time just before you went portable, and create a new account for home operation that starts after you got back.
4c. I'm not sure what to do about QRZ, HRD, or any other electronic system as I don't use them.
5. Finally, if your log program automatically uploads to any electronic system, do NOT let it do that with these QSOs. That is the equivalent of sending paper QSLs from your home QTH. The right way to partition the QSOs depends on the logging program--some may let you set station location by QSO, others may make you create separate files, etc.
From: Bryon nnegrom@...
To: 070 <070@...
Sent: Sun, Jul 30, 2017 2:27 am
Subject: Re:  DM49 Coming on the air!
Maybe I messed up. I didn't use /P
What would have been the best thing to do?