weatherproofing an ultrasonic sensor

I am using a maxbotix ultrasonic sensor and i dont know how i can make it rain/wind proof

i do not have the weatherproof version from them, just the regular version. (cost is way too much)

but right now i am not really sure how to let the signal pass through an object while the object is in front of the membrane.

I heard that there was some foam you could use but i couldn't find any pictures....the forums that maxbotix pointed me to had threads with broken links for pictures