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
2006 Ford F150 Super Cab 4x4
2008 Surveyor 263