Even with that year, there should be a sticker in the cabinet over the sink that state the weights. The current 2502S lists a 3950 lb. weight, and that is before options. I doubt very seriously that a late 90s 2502 would be lighter, though it might not have the weight of the slide.
If there are no weights listed in the cabinet, or in the lower front drivers side corner, ask the guy if you can see the title.....that should list the empty weight.
Chap , DW Joy, and Fur Baby Sango
2017 F350 Lariat CCSB, SRW, 4x4, 6.7 PS
2017 Grand Design Reflection 337RLS