Waterproof is a dangerous statement if you're going to use an external connection with a jack. Water resistant at best when you're dealing with boat splash. Removeable silicone caulking can make some decent "almost permanent" seals on jacks. Just be very careful with the amount of strain on the jack, nothing sticks to that radio rubber well and if your rig becomes separated from your body, that jack and some silicone isn't going to help.
In terms of audio, how about a noise blocking earpiece?
I use these:http://www.amazon.com/AO-Safety-99014-Blockade-Isolating/dp/B001HVC8QU
- AO Safety 99014 earbuds.
They work great high noise. They do get a bit uncomfortable after 4+ hours, just like any other plastic earplug. You get a solid seal on the ear canal and very clear audio. They come with a few different removeable caps.
I have managed to clip the earbud leads and solder/heatshrink them onto other audio toys. Less sanitary, but boy do they work well in noisy environments.