On the interior ceiling strip, the translucence is normal (fiberglass will let light
in normally, unless it's painted), but it wasn't put there to let light
in. Normally there is a strip of carpet there (in the gap between where the two inner shells join on the ceiling and running down the walls). Some people keep the carpet and some re-fill that area with white plastic, naugahyde, or wood. One can insulate under the new covering (nothing against the original carpet, but it's nothing to mourn the loss of if it's gone).
Some Burros were insulated between the shells and some were not - I think it was an option. The trailer will probably "glow" inside in sunlight anywhere where there is not insulation (so perhaps "yours" is insulated if you only saw light at the ceiling gap).
As to the outside, it's a bit harder to answer without seeing it. Fiberglass can always be repaired - it's not even too difficult to do yourself if you're interested in learning - but matching the original gelcoat can be a bit of an art. If it's painted, or if you aren't bothered about a perfect match, then it's easier. It probably wouldn't cost an arm and a leg to have done, but it's really hard to say from just your description. Boat or Corvette repairers would be able to give you an estimate (or show us some photos).
These campers were built to be light, so many of them will flex to some degree if you push on the outer shell; not necessarily a problem (again, generalizing).
It's possible for water to get between the shells if the trailer has had unaddressed leak issues in the past, especially if they were long term. I would think you would smell must or mold, but perhaps not in cold weather. Also, the floor is wood encased in fiberglass, and although many provide trouble-free service for years, it is a place to check for rot.
Many people like the Burros (and U-hauls) because the "double hull" gives a nice, shiny, "wipable" surface inside (other brands have either carpet, marine fuzzy material, or vinyl covered foam on the inside (to name the most popular treatments).
There are Burro
photos you can access from the home page here, if you haven't seen them, and in the Document Center (look on the left margine of this page), there is a link to a Buyer's Checklist you can print out.