The VXL is is billed as being 'water proof' since it has a sealed case complete with O-ring seals. It aint watertight though, but it does have a conformal coating.
The MMM makes too much power and handles too many amps to be completely sealed- it needs air cooling so hence all the vents. It does have a conformal coating too though, so it offeres a degree of protection; if you wanna get your model wet, buy a boat is what I always say.
I do lie the German dude's idea- makes it look rather like an old Mtronics esc....