The previous posted "aitaonline". Also they have a "low clearance" app plus the truckers atlas lists low tunnels and bridges. However, some of the biggest problems is the power lines within RV parks. I only had inches to spare under a power line in a little town in Washington near Mt Rainier. Just be careful when off of the interstate. My wife got out and I drove slowly under that power line.
Sometimes in low tunnels highway 14 north of the Columbia River near Lyle, Washington you can take your lane out of the middle when no oncoming traffic.