Hi,
No warranty express or implied with this, since I don't use my GPS quite this way, but ...
Last year when I went looking for a GPS for an assortment of things, I ended up selecting the Garmin 76CS.
It is clearly designed for hiking applications and such, but is also capable of marine use and driving use. At the time it was in my opinion Garmin's top of the line handheld, and did everything they offer except aviation ...
It is "waterproof" (read details, as aways with such!); does road, topo, and marine map products; has outback use features like sunrise/sunset, hunting and fishing guides, compass, altimeter; and has a big memory (there was a newer model with more cool-looking rubber armor, but it was the same guts and features with less memory).
Decent Windows PC software and cartography support online also. Maps will cost ya, though. The maps I have used have proven quite accurate.
Give the Garmin's a look.
Cheers,
Walter