not necessarily I've owned my Galant 3 years now had to drive thro flood water once a few years ago, up to bottom doors also done a bit of dirt driving etc but has never missed a beat or had any issues with starter etc. wouldn't hurt for extra protection but not necessary IMO
I took mine off, pain in the butt when servicing, especially as I do it every 5000 and I don't have a hoist. Driven through some flooded roads several times (slowly) and never had an issue.