There is not enough room to place 30lb tanks in the stock location and still allow for the front bunk to open. On my Roo 19 there would have been no issues with hose length, or the length of the threaded rod for the hold down though.
I moved my batteries inside, for various reasons, and this allowed me to move my LP tanks back and place a tool box where the tanks used to be. By doing so it lowered them also. When I measured there is now just enough extra height to use 30 lb. tanks
The neat thing is that the original cover for the 20 pounders sits on top of the frame still so the extra height is underneath the cover so you don't need to change it either
We just got our Roo last September and I still have the 20lb. tanks on it but I could change them out now for a long trip. The other thing that I have thought of is on a long trip you might want to take one 30lb tank and your oldest, crudiest 20lb. tank. That way you don't have to search for a fill station on the road but can just exchange the 20 pounder wherever is convenient.