I love my Prusa i3V but the stock spool holder leaves much to be desired. It obstructs the access to the SD card, it makes strange noises with some spools replacing spools is a hassle due to the design of its cross member and its height makes it more difficult to cover it with a box to control draft. Clearly a better design is required.
This thing moves the spool from the top of the printer to its left side just behind the z step motor. It is made of three parts, the spool holder, the filament guide and a round spacer that matches the stock M5 screw that comes with the Prusa i3V.
The shiny cylinder part of the filament guide is a short stainless still I found in a local hardware store (The Hillman Group 1/4-in x 3/8-in x 1-in, Seamless Steel Spacer model 880416). It is hold in place with two M3 screws from both side. The cylinder can turns but it's not critical as long as it is smooth. I also wrapped kapton tape on the main spool holder to reduce friction, probably not required but doesn't hurt.
The main part is held in place with 4 M3 screws. Use small washers on the plastic side (they will sink into the base) and large ones on the wood side. Make sure to position it such it can accomodate all the spool sizes you intend to use without touching the Z step motor (remember, the Z step motor moves up and down and should have enough clearance in all positions).
Printing is straight forward I printed everything with PLA and no material support.
All sources files are included so if you need to tweak it modify the relevant file and regenerate the STL files in openscad. My printer has 8" x 8" hotbed but I think it should work with all i3V versions.