Yep factory air filter.
I do make a point of leaving the house clamps loose though, so if it does backfire it'll pop the hoses off.
I don't know a lot pv charging, but you'd need some sort of regulator I imagine.
I'd join it to the battery; you can still camp for 3 or 4 days in the same spot on one aux battery with no charging - we've done it quite a few times. Just fridge and led lights.

