It seems like the best option to avoid damage to the plastic body when going through water is either the Delta3dstudios WPA (which isn't hard plastic) or some 7/16" OD - 5/16" ID Food Grade Silicone Tubing with the mouthpiece removed/over top of the stock mouthpiece?
A local brewery shop has some of that tubing so I'll probably go that route as it's the cheapest way to prep myself for using through water in case I want to try it out.
For tryout purposes, tubing on the mp is a fine way to go, but understand that you'll lose some potency with such a long vapor path. Cooling/condensation take their toll, while they also smooth, moisturize and cool the hits. The cooling unit is redundant when using water piece.
I use the delta3d adapter. While not perfect, it is not a strain on Mighty's plastic. The silicone-on-glass connection can get slightly stuck, so it needs a little wiggle to remove, but other than small accommodations like that it's a very good choice. He's got a sale going, of course.
So many available now! Used to be we made our own, the muzzmod, just before the walk to school in 3 feet of snow.