Hooray to Cryptozoology!
I haven't really heard of a Chupa Cabra looking like a bunny, but I think your trying to adapt the blueish-white kangaroo with fangs description.
But how about trying these other descriptions:
Grey Alien Bodied (you should be familiar with the big-heade grey dudes with wide beady eyes)With spines on back and a elastic webed skin fold stretching from the wrist to the waist, and ofcourse... fangs.
~o~
Or maybe...
Baboon shaped body again with spines at the back and fangs.
~o~
some say the spines at the back of a Chupa cabra can change its colors voluntarily
~o~
you also forgot the fact that they have the ability to fly with the stretched skin at their sides.
~o~
Chupa means sucker
Cabra means goat
put together and its Chupa Cabra! the Goat Sucker!