It's the big windshield and no hood or fenders out front that has you spooked. You don't have any reference points to judge the size of what your driving. Yes it is larger than your class C, but not by much. Just remember when driving 4 things:
1) Aim high in steering, meaning always look at least a 1/4 mile ahead of you. Do not keep looking at the side of the road to judge your spacing in your lane. Always look way ahead and you will automatically keep the coach centered.
2) Keep your eyes moving. DO not stare at the road in front of you, constantly check your mirrors and gauges.
3) Get the big picture. By constantly checking way ahead and your mirrors you will develop a "picture" of the traffic around you.
4) ALWAYS leave yourself an out. Never get boxed in when in traffic. Either speed up or slow down so no traffic is directly beside you at highway speeds. NEVER NEVER follow the vehicle in front very close. Always leave at least 4 to 5 seconds between you and anything in front at highway speeds. In an emergency your best "out" is your brake pedal, but only if you have left enough space to get stopped.
If you follow these 4 principles of defensive driving you will find the coach will be a pleasure to drive and not nearly as scary.