The other option that I thought of is to use two of the tubular ones, and mount them inside, at the aft wall, corners of the cabin. Using two, to increase the return image, since they are less effective than the tri-lens units. That would be less expensive, mounted inside, so less to worry about as to windage, and wear when the cover is on.
Harvey
SleepyC :moon
Harvey
SleepyC :moon