The 3051 has so much internal storage that we actually don't use it all. The cabinets above the sofa were pretty much empty for the first 6 months - now we store extra supplies of plastic cups and plates up there with a few sofa throws, too.
We use the space under the sofa for 12-packs of soda, and some wine storage with a wine bottle case laying on it's side.
I put gas pressure springs on the storage under the mattress to make that usable but it's empty most of the time.
We had a 26' travel trailer before the Forester and after moving everything from the TT to the RV we had only utilized about 60% of the space and that was everything we needed.
One thing to keep in mind is weight considerations. There is enough room to overload the RV if you really fill it up.
2015 Forester 3051S
TOAD: 2016 Lincoln MKX