"Kentucky Max"....I've done a couple of different coaches over the years, but nothing as a big as a 40'. Typically, the carpet is installed and the cabinets are installed over it, so it will have to be installed differently than it was originally done.
I would find a local carpet installer and see if he's willing to do it as a side job. A local RV dealer might have someone they can recommend.
One thing that is nice, you can cut along all of the cabinets and remove the entire carpet making a perfect template for the new carpet. Often, thin padding is used to keep from having issues with doors and slides binding up. If you have no slides, using a nice thick padding will give you some surpisingly improved sound deadening and insulation. You'll also find that they typically use about a 1000 staples when installing the original carpet. It took longer to pull all of the staples than the total of the rest of the instalation. If I wasn't so anal, I should have jsut flattened them with a hammer.