1200 lb with water tank empty and trailer unloaded may be accurate. Or might not, depending on how it is set up. Height is normally under 7 feet (barely) but depending on tires
could go over. Length is 13' overall, width about 6 feet.
I think (don't quote me) the Compact floor is not fiberglass, so check for rotten plywood, especially by the door. Check the pop up mechanism and see what condition the fabric is in. Replacing it can cost $200-$400. Same for cushions and cushion fabric. Leaks
would be at windows
and anywhere there is a vent. If you smell mildew it has probably been wet. Leaks
aren't all that common, though, and many Compacts have been stored in garages, unlike traditional trailers.
Someone else can tell you what to check for on the frame as if I recall, there can be weak spots. (Or use the search on this site (but search google) to find compact frame.)
The doors on these are notorious for bouncing open while you drive so don't be surprised if there is some kind of door-holding device. (If not you may want one.)
There is a full checklist in the documents section but these are things I can think of which are particular to this style of trailer.