As a 21SS owner, I can't help you with the measurements either, but I had large carpets in my Rockwood Popup (helped immensely with the cold when camping in Novembers). However, I only have two (bathroom rug and entrance rug) in my Roo. I bought Shaw carpet throw rugs at Meijer, and they wash well. I bought a Shark Rocket vacuum cleaner to keep in the camper, and shoes are not worn at all in the camper, so dirt is kept at bay.
I would wait until after delivery; you can measure exactly and more easily shop for matching colors.
The rug I got for our bath is very plush, but unfortunately the luxurious pile also causes it to dry slowly. I would suggest looking for a quicker-drying rug.
I don't use any rugs in the main area, as the 21SS is already carpeted on the slide-out area.
2014 F150 SCrew 4x4 Max Tow Heavy Duty Payload 3.5 Ecoboost 6.5' bed Ingot Metallic Silver
2015 Rockwood Roo 21SS