For the price of that well cell, 500$, I would patch 90* strips the corners of the wheel well and fit a square cell in the hole. Obviously this would be cutting up the trunk floor though
When I ran a cell I had a sheet metal up made to fit it. Cost me maybe 150$ for the tub and I cut out the trunk floor and welded the tub in then mounted my cell in the tub. It sat down as far into the trunk floor as possible and then I had a cover made for it.
Lots of money and work and time. Wasted....
buy a factory under mounted cell and be done with it.