Replacing wheelhouses

Do the outers first and use the inner to locate the outer. Sheet metal screw the outer in place then remove inner. After everything is fitted then you can start welding in. It will be much harder to do if your trying to save the quarter panel. Typically you would be replacing the quarter at the same time since its probably rotten too. But anyway, I like to use original undisturbed metal to locate new metal anytime possible.
I dont think mini tub would make the job any easier. It will require fabrication which could make the job more difficult than just a straight up replacement.