I would say at that point your best bet would be a Provari with extension and a 4 up battery charger. 8000 mAh is a lot of battery life. Yes, it's replaceable battery, but it's probably the simplest and safest setup period, even including the non-replaceable battery systems.
Just buy from them and no worries. I have an MVP2 and love it, but if you're looking for longer life, then you're pretty much stuck with replaceable batteries.
Another option which I haven't tried but might work is to get a large backup battery like they make for cell phones and tablets. You can get reasonable sized backup batteries up to 10,000 mAh. If it will charge a big tablet, it should charge your MVP no problems. (Anything that will charge a high end 2.1 A device should charge an ecig battery.)