For motoros I would recomend somthing along the lines of 98''x48''x24'', and a big female can even make that look small.
If you have to have a smaller tank, there are some ray sp. that are suitible to live in a 180gl for life, like histrix, scobina, and retics. Retics are easy to find, but if you want the the other one of the other types it will take some searching.