Not fully enclosed. The bottom and the entire other side is open.
The idlers have washers on both sides, but are not gorilla tight and don’t need to be.
The 608’s need 8mm post to ride on comfortably, these offer a smaller overall machine, and less hardware. Space is tight in the belt area and I’m not just talking about my belly. They made sense in the MPCNC because of where the motor sits but on this it’s different. I also have to account for various panel thicknesses so all dimension critical mounting has to be done on the same face.
It is still looking like a thicker table is going to be a better option. Of course you can go custom but I am going to start by recommending 3.5-4″ (or less) thick in the longer rails. The wheels will hit about 1″ from the edge, so far, I am still actively changing that part right now.