Yes, 5000mAh should get you a couple days at 30W Or, at least a day if you chain-vape like crazy, lol... I'd snag two if I were you, so you'd have one to vape while the other is charging... or at least carry a couple of other backups that you can use while the iPower charges. Personally, I just carry several extra batteries when I travel, swap them as needed, and charge them in the evening (at the hotel).
You say you don't have a 12V charging plug in your SUV? That's not a huge issue, as you can easily add in a 2A USB plug (many of them look like factory plugs once installed) for about $10-15 and buy a Nitecore U20 charger... it's like the d2, but connects via USB, rather than standard AC plug (although you can use a AC/USB adapter). They work best if you have a 2A or higher USB outlet, and are fantastic chargers... I have two, so there is always one in a vehicle or my travel bag. They're worth every penny of the $15 each I paid for them on Amazon
As for tanks, yes the Toptank mini or the original Subtank mini would be good. They have good airflow for lung vaping, hold ~ 4ml of juice, the coils are not "expensive", and I've yet to have one leak that wasn't MY fault... left one in a hot car and I failed to fully seat a coil in the base once