tjbaudio:
Is your project a large one or just a one off? I ended up getting some PCBs printed for mine.
Mine is just a prototype. Still no custom made PCB.
Yesterday I came to a different approach: I added a much larger heatsink to the 7805 powering the sistem. And suddenly the temperature on the 485s dropped. Looks like heat was traveling throug the cables and traces 
Now I can feel that the hotter one is the one transmitting more data. Next experiment will be trying to lower the data rate.