I think it's quite possible he'll have a net positive rating sooner or later, but I also believe his ceiling is historically low for an incumbent president. He might not ever have more than 55% or so of Americans on his side, unless something cataclysmic happens, like a terrorist attack on the scale of 9/11.
Excluding the "honeymoon period" during his first six months and the "riding off into the sunset" period during his final month or so in office, wasn't the same true of Obama? Sure, there were a few individual polls where he was above 55%, but when else was the polling average for him higher than that, excluding the very beginning and the very end? Trump of course isn't getting the same kind of early honeymoon period that Obama got, but I think if he follows the Obama trajectory from the middle of his first year onwards, he'd be very happy with that.
He was around 55% for pretty much all of 2009 and around his second inauguration, but your pretty much right in that people were split on Obama for most of his presidency.
