Glass tops are the safest way to go .... although I have removed mine due to hard water deposits.
You main worry is water getting into the connections & causing rust. you can replace the normal shoplight endcaps with water proof ones. For the rest of the connectors, I wired my shop lights so the ballasts are outside of the canopy. <Canopy is oversized at the back, with space for the ballast.> All the connections are made in a plastic outdoor water proof junction box so I have no exposed joints. <This is good practice even when you are not worried about water ... It makes me cringe when I see the shoplight mods on the web where they have all their wire nuts exposed inside the canopy ... That is an electrical shock waiting to happen, esp. in wet location .... And for extra protection, my lights are plugged into a GFI outlet. Alternatively, you can wire the GFI into the canopy.>
I have my canopy running for 3-4 years now (glass top removed for 2 years), no sign of rust anywhere .... Note that my entire back of the canopy is open for air circulation so there is also not much condensation ... although the joints are all water proof so that doesn't matter much.