Actually no need to print the kevlar fibres, you can just insert that layer manually
..that is if you print the belt flat, which unfortunately will proove to be nearly impossible on a common 3d printer
(you'd need a fourth axis that wraps around the printbed, like the continuous belt bed from early makerbots)
but in the correct size for the belt length you need of course... (said it's nearly impossible, right?)
Then you could -in theory- print the backing,
and while the bed-belt moves along, you can add the kevlar enforcement on the edge of the printbed manually, as it loops around it should then fuse with the next printed layer.
It's still likely the worst possible belt you could install onto a TAV,
and not the cheapest either (considering a small spool is maybe good for two belts and costs around the same as two commercially made belts)
Ask Slic3r for the amount of material (or whatever slicer you're using) and do some math
you'll see what I mean
For small flexible parts it's actually fairly easy to reinforce the part with duct tape or such manually... long belts -or worse continuous ones- however are tricky to say the least.
'sid