I forgot another solution to increase deep water crossings: speed.

If you can stay on the surface long enough you can cross very deep waters.
Don't laugh: In Iceland they have races that cross deep rivers and ponds
where vehicles have to manage to stay on top of the water long enough. They
do that with maximum revs and very wide tires. The trick is to have the
right speed and the right rpms without blowing the engine. Some do sink
among the cheers of competitors and spectators. It can be expensive.

Admitted, the vehicles themselves look pretty outlandish and it would
require substantial modifications to make a vanagon do the same trick, but I
thought I would consider any option. 

:)

Bj�rn