I don't think there can be any cut-and-dried answer on a 30+ year old trailer. I say that because of the wide variation in real (measured) weights on models that are similar to each other (Scamp 13 vs. another Scamp
13, for example). Varying accessories, batteries, tanks, flooring, etc.
In addition, most if not all of our older eggs weigh more than the factory claimed them to.
If I remember correctly, the Trillium
4500 was said to weigh around 1400# from the factory (I forget the exact figure, but I think it was 200# more than the 1300). I would be surprised if many weighed that little, especially a bathroom model. And of course they have more stowage, for more gear, than a 13-er.
My "light" guess would be somewhere in the 1600# range, without personal camping gear. More if bathroom model, two propane
tanks, multiple batteries, full water tank, etc. I would think that it would be unsuitable for someone with a 1500# towing capacity, rather close (loaded) for someone with a 2000# capacity, and easily fine for someone with a 3500# capacity (these being common tow ratings).
In the end, if I were close at all on my tow rating, I would want a verified (scale) weight
on an individual 4500 that I was looking to buy or tow.
Maybe a member with a weighed 4500 will chime in