If you throttle is like the one on my Monaco coach the connection to the engine is electrical so moving the pedal to the left, along with the electrical control, should not be too much of a problem. Moving the brake pedal may require cutting off the old pedal and fabricating an offset piece that can be bolted on the the existing brake pedal shaft. Not that big of a deal.
I would not want to do any welding under the steering column inside of my coach.
If you move the seat, it may position you off-set to the steering wheel as well as more distant from any left hand switches, etc.
Just figure out what you need to do and then remove your seat. At that point access should be pretty easy.