An alternative to mounting speakers that have greater depth than is perfect (won't fit in cavity), is to use a baffle on the surface. The baffle is typically a circular ring that attaches to the surface and the speaker is attached to the baffle. These can be made of wood, plastic, or metal.
BTW, Pyle anything is about the bottom of the quality barrel. I'd suggest you make another choice. No sense going to the work of replacement and ending up with a sub-standard sound.
Just thinking here but if a user didn't want to cut out larger holes in an RV wall, it would be easy to find a pair of enclosed speakers and just mount a conventional two-wire jack on either the wall or the original speaker grill. Enclosed speakers would probably be an upgrade in sound quality and can be positioned anywhere (like close to the listener). The downside is that the boxes need to be connected and disconnected for normal travel.