Measure the cabinets already in place as well as the total available area to be used. You may have to use different-sized cabinets if you can't replace the old ones with the same size. Observe construction, such as adjustable shelving, and where original holding screws are placed. Note how countertops are installed, because you will want to replace those, too.
Purchase laminated cabinets rather than cheap wood or particle-board cabinets from a local home improvement store if you have a small RV that opens up. Laminated wood is a great cabinet material for its ease of keeping clean with a simple wipe-down. Laminated wood weathers different climates and humidity better than wood or particle board, especially if you like to spend significant time at the seacoast. For larger RVs with central air and heat, use any strong wood you like, since weather outside will not matter when you have climate control inside.
Remove your old cabinets, noting how each one was installed, and replace with a new cabinet. Secure with bolts to the flooring. If replacing a sink cabinet, make sure pipes and hoses have free access underneath and through the back before bolting down. Once your cabinets are in, take a measure of the cabinets' top dimension and either purchase a laminate countertop and cut the sinkhole yourself, or order it from a home-improvement store and have it cut for you.
Add in more shelving as needed by adding in holes on each side and resting shelves on shelf pins. Alternately, you can glue, then nail on ledges on each side, then just slide the shelf on top of them. Put in a restrainer nail at the back wall to hold down the shelf so it doesn't tip. Use sliding bolts on cabinet door fronts to hold doors shut while the RV is moving. Add rubber shelving sheets to keep items from slipping around, particularly your plates and cups.