The problem is with how you use your batteries, not the device.
The corrosion is the result of out gassing, all batteries out gas over time but a dead battery out gasses most. Heat will increase the amount of out gassing so don't store the batteries in warm or hot temperatures if you can avoid it, whether they are in the GPS or not. In the military we always stored our batteries in a refrigerator (OSHA recommends that you don't store the batteries in a refrigerator that has food in it) and even now I store mine in a cool spot in my basement.
When you aren't using the GPS remove the batteries, that will prevent the corrosion problem. If you like to keep the batteries in the unit then use lithium-ion batteries and connect the battery charger to the GPS. Try to not let the lithium-ion batteries go below 40% charge.
In order to make the batteries last longer during use make sure that you are only using the features that you need, don't run the weather alerts and such unless it's really necessary. Reduce the brightness of the display. Delete unnecessary waypoints. The biggest issue is that people think that a GPS is designed to be used 100% of the time, they are not. You should be using your GPS as a tool that you refer to from time to time, don't leave it turned on all the time, try to use it like you would a compass, you don't hold the compass in your hand 100% of the time, you simply use to identify a ground feature that is your target and you walk that direction until you reach the target and then you check the compass/GPS again for the next target point. I don't leave my Rino 650 on for more than 15 minutes or so at a time and that's usually when I'm traveling in my vehicle and trying to locate something. While walking I don't keep mine turned on for more than a couple of minutes at a time.
