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.
Baboon shaped body again with spines at the back and fangs.
some say the spines at the back of a Chupa cabra can change its colors voluntarily
you also forgot the fact that they have the ability to fly with the stretched skin at their sides.
Chupa means sucker
Cabra means goat
put together and its Chupa Cabra! the Goat Sucker!