I've wondered how to waterproof an alternator myself. I would love to just buy one of the waterproof ones but they are a little too much $$$. Although now that I've read your post it reminds me that I do know a couple of guys that could point us in the right direction. Makes me wonder why I never asked them before. I'll let you know anything I find out as soon as I can get ahold of one of my buddies.

 

i spray mine with silicone a few times a year

 

silicone dry lube the crap out of it and stay out of deep mud. That is the only way to protect it.

 

So forgive me because I know next to nothing about alternators - is there no way to build an enclosure? Maybe not totally air/water-tight but some way to offer it a little more protection? Or like a splash guard, for lack of a better word?

 

^ skidplates work pretty well. Aside from that you are wasting your time. The heat generated by the alt and the difficulty and crammed nature of it's locale offset even the most optimistic hopes of creating a feasible splash guard. It would be difficult to implement for little to no benefit IMHO. The stuff that is going to kill your alternator isn't a splash of mud or water here or there....it would be constant immersion or steady introduction of gunk into the brushes and windings....a "splash shield" would be of little to no help. You best bet is get skidded up. I ran for 4 and a half years through some serious mud and water before I had to replace my alternator.

that's just my take on it....

 

I'm still on my first one! IT does squeal like a pig once in a while though.

 

I used some rubber sheeting and sealed off the passenger side fender liner. just to limit amount of mud splashing it from wheel well. I have thought about making a shield under it as well. But full skids would protect better.
I'm on my 3rd alternator. The last time I pulled it apart myself and replaced the bearings. It only cost me $10 for bearings from the local alternator shop. I never had the brushes go bad. It's always been the bearings and every time it was from a wattery, sandy, mud mixture in a certain mud field that has claimed many Xterra alternators. I have gone through deep water that is slightly muddy and never had a problem. It come down to the texture of the mud that will kill ur alternator. Here's a video of the alternator killing field I speak of.
http://i499.photobucket.com/albums/rr356/acasper708/268872bd.mp4
Later that day Kelly needed a new alternator!

 

Also here's a pict of my X thoroughly covered in mud. It was very fun!!!

About a week later I needed a new alternator, throttle body, and blower motor!
So I don't play in mud that much anymore.

 

I've crossed the 30-40" deep Mojave river about 8 times and it's not the water that kills the alternator but the mud apparently as I haven't lost mine yet.