It really depends on the vehicle. Most class A have room to do the install versus say a class C that is on a truck chassis.
Get a good set of headers to start with. Ceramnic coated are probably the best to help remove the heat from the engine compartment.
I would soak all the old header bolts with some sort of penetrating oil, like PB Blaster or Kroll Oil. Breaking a rusty nut/bolt can ruin you day.
The next problem will be cutting and attaching the headers to the exhaust system. In many cases is easier and cheaper to go from front to back with a complete new system. If you remove the old system first, you can install the headers from underneath the coach, install the connecting pipes, cats, mufflers, hangers, tail pipes, then adjust for clearance and lastly tighten up everything.