The covers looks like a good product. Being able to check oil level or condition is putting the problem backwards, though, in my opinion. Not that it is a bad thing to be able to check fluid level, but it is not something that needs doing on a daily basis. First, axles should not leak. Period. So, where would the fluid go from day to day?
Secondly, axles should not leak the other way around, either, so crossing creeks should not pose a problem. If you have water intrusion, you have stock vents (read improperly vented axles). Remove the stock vent, insert a brass or steel hose bib, run hose to the top of the firewall or at least well above the depth of water you expect to cross, put the dust guard on the high end of the hose and eliminate the intrusion. I drove off road in Alaska for years, including regular water crossings in the 3 to 4 foot range and bogs deep enough to hide a Vokswagen, and never had water in the axles.
Same for the transmission and transfer case. Run vent hose to the top of the firewall and you should get no water in either of those as well.
Even if you don't expect deep water, venting axles and driveline to a secure location will improve air quality by putting the vent away from dirt and dust.
