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 necessary.
If it had been flat or, if it was, did it stay level leveling the mattress has always been a hit and miss thing, you never knew for sure. Now it does and it's so much easier to do.
Cost: $7.10 + freight and some filament.
I purchased 2 bits of 2020 aluminium section x 500mm long from Aliexpress.
Print both bits from PLA at 0.2 layer height, with 50% fill, no support is required.
The Rail Spacers includes a skirt and the Bed Support includes a 5mm brim.
When printing the Bed Support recheck your mattress for level and up the bed temperature a little, being such a large piece I had some lifting at a corner that is OK now.
Printing the Rail Spacers from the same color filament, and off the exact same roll or you may find a slight variation in size.
Possibly the most difficult part for some will be drilling the holes in the carriage that is oil.
The secret is to use negative rake drill bits (see picture). You can do this yourself by squeezing the sharp edge or rubbing the border with a grinding stone. If you do not do so, the drill will catch the oil and you may brake it. Practice first on a scrap piece.
Drilling the holes.
Twist the Bed Support on to the acrylic carriage using the 4 holes, with M5 x 20mm bolts, washers and nuts. Drill all 4 wheel mounting holes using a 5mm drill first, using the Bed Support for a drilling template, then re drill 2 holes with a 7.5mm drill. Be sure that you drill them in the location, see picture.
If you stuff it up you can find 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 2040 using M4 x 10mm screws, and nuts.
Re assemble and level.
Some of you will have notice so that the smooth part of the belt now runs on rollers, the belt at the front has twisted, the motor end stays the same.