Steam Gun Boats spent displacement on protection

How could a Steam Gun Boat protect its boilers in a close-range fight?

Its roughly 275-ton displacement allowed some protection around the machinery, unlike the far lighter boats that could carry little armor.

A viewer points out the danger of high-pressure boilers being penetrated during a small-boat action. The Steam Gun Boat's roughly 275-ton standard displacement allowed protective material around machinery that a lighter MTB or Schnellboot could not afford. Its unusual size was therefore part of a design tradeoff between speed, weapons, and survivability. The displacement was not simply wasted bulk.