I'm not so sure you'll find all you answers in the code book. How far flammable conductors can go into a building is usually a local code issue. The length could be 0, a few feet, or maybe 10 feet and may require metalic conduit. If this is dual rated, then there may be no length limit, but you'll probably need to talk to the inspector.
Physical protection is also typically an inspector call.
PVC has to be buried 18", and USE would have to be 24". To go less than this requires rigid metal or concrete. If the culvert is a "driveway", you may have to go 24" regardless of how its protected.
You may not have to seal a conduit. USE is rated for direct burial, so it can get wet. You would have to seal the raceway if it was outside and entered a heated building since each end is exposed to different temperatures.
