Why not rent a micro-dolly? A slider that long is probably more troublesome to transport and assemble than a dolly. BTW Camwerkz and CRC has Hollywood Micro-dolly
For extreme low angle you can either:
A) use a long 3/8"-16 bolt and a washer to attach a ballhead/small video head directly on the microdolly or
B) use a friction arm to clamp the camera to dolly.
C) use a low-spread tripod or high hat on the dolly
I'm not sure what you mean by 45 degrees. But you use a slider (vertically on a tripod ) and a dolly together to create 2 axis of motion.
At the correct speed of travel, the path of the camera can be 45 degrees.