Is your bed north/south or east/west? The reason for the question is converters tended to take advantage of the bed to accomplish some things.

An east/west bed may have a safe, heaters, or even some other systems beneath it. If the bed is removed they also need to be removed or they need to be covered somehow.

A north/south bed may have all of the above, and it may also have been used to cover the engine access panel on your vintage coach. It is no big deal covering the engine access panel with carpet, but it should be removeable. It should also be able to seal properly because a poorly installed engine access panel is going to introduce a lot of soot, rubber particles and fine dust and dirt particles into the coach.

There is no problem with what you propose as long as you can work around the minor stumbling blocks.