I've got a GPS72 and though I haven't figured out how it all works yet it seems ok and is supposed to be waterproof.
Regarding battery life I'd add a cautionary note about believing manufacturers claims - I also have an eTrex (basic "yellow peril" model) with a claimed battery life of 22 hours - not a chance! - half that if you are lucky though I've never measured it. The eTrex is supposed to be waterproof except for the battery compartment which isn't, so if you drop it in the oggin all you'd need is a new set of batteries.
Mapping GPS's are not a lot of use here as the base maps are a bit restricted. I was driving a visitor around the Islands a couple of weeks ago with a £500 odd fancy mapping GPS he bought to record where he'd been. The base map of the coastline of East Falkland (island measuring about 50 miles NW/SE x about 100 NE/SW)was made up of about eight straight lines so he gave up after the first day because it kept saying we were in the water