I don't see the need to cover them.They are pretty much covered the way the are.Dust and pollen are at the worst in the spring and people don't cover them then,i dont see the need to do for winter.The reason for covering a home AC unit is that they are open from the top where the fan is and you don't want snow and ice to build up inside them,that being said I haven't covered mine ever and it runs fine.
06 2500 Duramax. Air lift 5000 air bags,Equalizer WDH, EFI live,fass fuel system,4" straight pipe
2015 Jayco Eagle Premier 314BHDS
IBEW local 94 Electrical Worker