If your rig is like my 2002 Itasca Suncruiser 35U, there will be a full-length plywood "ramp" about 4" deep under the slide at the wall (see link below). It's purpose is to raise the inboard edge of the slide when it is extended, "cocking" the slide so the weather strip is compressed at the top more than lower down. If you have this, you may be able to see it by looking from the outside underneath the extended slide by pulling back the bottom seal. It also may be visible as a hump in your old carpet inside your coach at the ends of your slide against the wall (ends are clearly visible when carpet and pad are removed).
My suggestion is that you not try to remove the carpet on top of this ramp but leave it in place. Just remove the carpet and pad up to the inboard edge of the extended slide (or slightly underneath the slide by angling your knife). Then butt your new floor up to the old carpet and cover the joint with an appropriately colored metal transition strip to keep the glide from messing up the edge of your new flooring.
My reasons for doing this are:
1. It preserves the pre-existing height of the lift provided by the carpet covered ramp so the top weather seal is appropriately compressed when the slide is extended. Your new floor will not be as thick as the old carpet and pad.
2. Removing the old carpet and pad from the top of the ramp is difficult at best since it's under the ramp and is stapled to the ramp. It's also easy to damage the plastic part of your glide (don't ask how I know this). If you do so, the glide could damage your new floor.
3. Your new floor will be thinner and leaving the carpet and pad in place on top of the ramp will mitigate the chances of depressions from the glide strip on your new flooring.
See this link for some photos (glide strip is on pg 2, ramp is on pg 3):