I grease them on the hard.

You're right, just removing the hoses would be a pain in the neck. I've never tried to grease one in the water but some of mine have grease fittings. It might work and is better than nothing.

I just take the nut(s) off the shaft and pull the body out. Clean it with a rag, grease(I just use water pump grease) and put it back together. They're all in easy enough spots and I know the contortion I need...

How often do you haul? Don't you have to paint the bottom every few years? I would think with a good cleaning/greasing and regular use, you could go a few years between full greasing.