On Series Rovers the wading plug (a 1/4" pipe plug) is installed before wading, then removed after, to help keep water out. The wading plug came from the factory screwed in to an 'L' shaped bracket attached by one of the bell housing bolts.
Provided you keep it removed during normal operation I can't think of any reason it would be bad to seal the bell housing.
If you do that, it's good practice to do the typical Series "modification" and move the bracket to the dash so there's never any question in your mind if the plug is in the flywheel housing or not.
Four wheel drive allows you to get stuck
in places even more inaccessible.
62 88 Regular
67 109 6cyl NADA x2
74 Lightweight - The Antichrist
95 DI 5-speed
95 D90 5-speed
97 D1 Automatic