I'd put it in the drain section in a corner away from equipment and drain if possible. You could also create pvc probe well(s) for them. Google search aquarium pvc probe well. Lots of DIY mods out there.
Yes, I was thinking about a box or a well. But I can't put them in the drain section. The main reason is the controller and the drain section is on opposite side of the stand (8' apart). I will need a lot of extensions. Also, I have micro bubbles there, and the plan was to put a bio-pellet reactor in that section when/if needed.
I think my best bet is the return section and a well or a box of some sort.