I recommend one of these Sherline ScalesThey accurately measure tongue weight on a trailer.
IMHO.. I would expect the tongue weight on that trailer to be closer to 600 - 700 lbs dry WITH camping essentials… such as the battery and two 20 or 30 lb propane tanks.
Many of those dry tongue weights are laughable because they do not include these basic essentials that ALL TT's travel with.
My POP UP has more actual tongue weight than your 28 ft's brochure weight. Mine is supposed to be 230 lbs.. bahahaha.. right..
Thanks!
Jeremiah