I believe your motorhome is a molded fiberglass shell, not the current fiberglass panel type. They do not delaminate like the panel type.
My 43 year old clipper is a molded fiberglass shell.
The main consideration is if the seams are on the corners or offset. If offset, then you are in good shape as the fiberglass shell is unlikely to leak at the seams. That leaves only the cut outs (windows, AC, etc.) sensitive to leaking.
The aluminum sided motorhomes are much more prone to leakage as they were usually built using multiple panels per side and had seams on the corners. Each seam and panel change is a potential leak.
The fiberglass shell will look nicer than the metal - allowing you to get into RV Parks that use 10 year old limits to keep out people they see as "trash".
Outside of that, your main concern is the quality of the house and chassis/engine. For a 30+ year old rig, those have more to do with upkeep by prior owners than manufacturer.