Don't know about the Keystone, but, As for the Apex. It is made of Azdel. A really lite composite material, and there is no wood what so ever in the walls. So nothing to rot. It also has a higher insulation value than normal laminate siding.
Only other thing I can say. Is it towes really good. Well balanced. Do lay in the bed to see if it is long enough for you. In our's we have to scoot up to the top. But then I have to do that at home as well.
And the bathroom entrance is a great thing, especially at the beach.
BTW. IF you plan on cold camping. Check out the furnace vents. Our furnace is under the fridge, and the main vent is there as well. There is another small vent near the main door, but not a lot of air comes out. However. The furnace does heat the TT very nicely, and is not so loud.