No, not fiberglass. That's a corrugated aluminum skin over a wood frame, classic stick-built construction.
Some "stickies" are slap-up jobs and quickly fall
apart; others are built well in small shops and can last for years with proper maintenance. I don't know if it's the same company that made the molded Oxygen
in the early 2000's, but perhaps someone else knows more. If not here, then a general RV forum or vintage canned ham group might have the information you seek.
It appears to be in great shape, but check carefully for water damage at the top corners inside cabinets. Once it starts, it's really hard to stop. If it's good, keep up maintenance on those seams, store covered if possible, and you can get many years of use.
It looks like a very nice layout for two people (and a small child on the overhead bunk).