The Tevo Tarantula double Y axis rails have made a huge improvement to the bed leveling and stability. I don't think the auto bed leveler is now necessary.
Leveling the bed has always been a hit and miss thing, you never knew for sure if it was level or, if it was, did it stay level. Now it does and it is so much easier to do.
Cost: $7.10 + freight and some filament.
I ordered 2 pieces of 2020 aluminium section x 500mm long from Aliexpress.
Print both pieces from PLA at 0.2 layer height, with 50% fill, no support is needed.
The Rail Spacers has a skirt and the Bed Support has a 5mm brim.
When printing the Bed Support recheck your bed for level and up the bed temperature a bit, being such a large piece I had some lifting in a corner which is OK now.
Print the Rail Spacers from the same colour filament, and off the same roll or you may get a slight variation in size.
Probably the most difficult part for some will be drilling the holes in the acrylic carriage.
The secret is to use negative rake drill bits (see photo). you can do this yourself by either grinding the sharp edge off the drill or rubbing the edge with a grinding stone. If you don't do this, the drill will grab the acrylic and you may even brake it. practice first on a scrap piece.
Drilling the holes.
Screw the Bed Support on to the acrylic carriage using the 4 inner holes, with M5 x 20mm long bolts, washers and nuts. Drill all 4 wheel mounting holes with a 5mm drill first, using the Bed Support as a drilling template, then re drill 2 holes with a 7.5mm or 7.0mm drill (you need to check this as some have 7mm hole and others have a 7.5mm hole). Make sure you drill them in the correct place, see first photo.
If you stuff it up you can get a replacement pre-drilled aluminium carriage from Isaac Frankhauser. http://fankhauser.me
The rest is straight forward, mount the Rail Supports to the new 2020 rails and existing 2040 with M4 x 10mm screws, and nuts.
Re assemble and level.
Some of you will have notice I have twisted the belt at the front so that the smooth part of the belt now runs on rollers, the motor end is still the same.