What will be important is the quality of the brake controller setup for your rig. There are steep grades in the 6-8 percent range but you can route your travels to avoid them to a large extent.
The interstates are one option as taxpayers pay a great deal to subsidize the trucking industry with their creation. The interstates are designed to minimize elevation changes and save trucker's fuel. Mountains have been leveled and valleys filled with dirt to "fix" highways for truckers in California.
Just get the trailer's brakes and wheel bearings and tires checked out before you leave.
The trucker models of GPS units will also recommend routes that minimize elevation changes though you may miss scenic areas if you let them dictate your route all the time. The Garmin is the favored unit by truckers.