The Dash 8-100 emergency exits are probably located in a rather forward location to keep them available when the (optional) moveable rear cabin bulkhead is moved to the most forward position, leaving only 5 rows of seats. The exit would then be in the second row from the rear, the rearmost probably being impractical because of e.g. the exit overlapping with the bulkhead.
AFAIR a Dash 8(-300?) crash landed during a bungled swingover in CDG in the early 90s and the wing spar came down and blocked access from the forward to the rear cabin. In a -100 that would have left you trapped in the rear cabin.
I don't think either the -300's or the -400's ditching dams have ever seen more water than a cup in the cabin or rain outside. The -400s dam for the airstair door is a rather flimsy piece that slides down from abvove the door and doesn't look very watertight. The right forward emergency exit is a two-piece affair where the lower part is blocked for ditching. The -300s inflatable dams sometimes go off in flight....