[scottkeen]

So one of the ideas I was thinking was to put the w/d on a sliding platform with full extension slide rails so I can access behind it and the plumbing supply lines and drain.

Here's a sketch up. The static load for the floor of where the w/d sits is 148 pounds and Splendide says the dynamic load is 280 pounds. So I would go with minimum 2x 140 pound load rated rails.

But as you'll see in my sketch up, the load is not so much on the rails, because they will be installed with the bottom edge right on the cabinet floor. Then when the platform is fully extended, the 1x4 strip of wood above the rails takes the load. There would be very little load on the screws that attach the rails to the walls.

This raises the w/d unit in the cabinet by about 2.5 inches. I think there's just about that much head gap clearance above the w/d.