Waterproof external speakers and sub behind bumper?

I'm working on a project that includes some sound effects that I want to play externally. I found some cheapish speakers and an amp from Pyle that I can mount behind the bumper. However...

After looking at the frequency response on the speakers, I think I need a subwoofer involved as well to make the particular effects sound right. (I'll post full details when I'm closer to done.)

I only need a 6.5" or 8" sub, nothing fancy and nothing expensive. I found a cheap sub from Pyle (6.5"), but it's not waterproof and I don't know what to do about an external enclosure. I also found an expensive warerproof, self amplified sub (8") that would fit in the space, but I don't want to spend the money on it.

Any suggestions on mounting behind the bumper or somewhere else for external sound, and how to weatherproof it? This is going in a 2012 Prius Two.

I think this is my last big obstacle in figuring out how to do the sound half of the project and would appreciate any help.

 

Someone just suggested an 8" bazooka tube with the sub replaced with something waterproof.

Does anyone know if that will fit in a 2012 base model? I can't remember quite how much room was there last time I had the bumper off.

SM-N910T ?

 

I was planning for the front bumper where there's more room. And I think I found plans to be an enclosure for a 6.5" sub that will fit.

SM-N910T ?