The Jackery is fine for a day or two. Base camp for anything longer and your wanting solar. I run 100 watts on my cruiser and 400 on my trailer with a 200 watt folding as a backup if I'm camped in the forest.
On my old trailer, my 150 watt put back whatever my fridge used over night and still had enough to run it during the day.
As for extra load on the alternator, if you used the alternator to recharge the Jackery, your still using the same amount of power. If I'm driving constantly then my alternator is my main. If I'm camping without sun, in just the cruiser, I have three days of battery before I have to drive to recharge.