Too may people shoot from the hip and state that the added weight is typically around 1500-2000 lbs on top of the factory UVW. How do they know that for sure? Did they weigh their TT when picked up at the dealer and then after everything is loaded in? I doubt it.
IMHO, 1500-2000 lbs is waaay too high, unless maybe they are including 4 full holding tanks. I think it's just another urban myth.
I am one of the few people that has actually gone through the exercise of accurately weighing everthing in a TT from the day it left the dealer, then weighed all mods and upgrades and finally, a weighing to determine the weight of all the camping gear, food & supplies, and all the other usual camping "stuff". We have an average-ish size of TT at 29' and 7000 lbs GVWR.
I used two separate commercial scales to weigh our TT and both were basically the same, so there was no error in the scaled weights.
I weighed our 2014 KZ Spree the day we picked it up from our dealer to determine the base weight before adding a single thing. When I got home, I found that the fresh water tank had some water in it, presumably from the dealer testing the fresh water system. I repeatedly filled a 2 quart container until the tank was empty and calculated the weight of removed water. I ended up with a pretty accurate base weight of our TT (less the weight of mods and any camping stuff).
Each and every single modification was weighed. Some of the mods were done by our dealer and I weighed everything (shocks, equalizers, roof vents, etc.) before turning them over to the dealer. Anything that was removed by the dealer was weighed and accounted for. Anything I did myself at home got weighed. Mods and upgrades included shock absorbers, Dexter equalizers, 4-stage water filtration, WDH snap-up brackets, 2nd TV in bedroom, and some others I've forgotten at the moment.
All the camping related stuff I weighed in the final weighing included all the usual stuff like BBQ, sewer hoses and fittings, folding table, chocks, outdoor mat, kitchen stuff like coffee maker, toaster, dishes and cutlery, at least several days supply of food for two, bathroom stuff, clothes, books, some tools, plus lots of other misc. things. Pretty much all the normal things anyone would have in their TT.
The weight of all modifications and upgrades came to a total of 119 lbs. I actually expected it to be much higher.
The weight of all camping gear, food, clothes, etc., etc. came to only 555 lbs.
So, if anyone says you add 1500-2000 lbs to the factory UVW, I don't believe it. That's 3-4 times what I got from going through the exercise of weighing everything before and after. You will also need to allow for the weight of the propane and battery or batteries and anything else the manufacturer may not include in their UVW. I would say that by the time you have everything loaded in your TT ready for a camping trip, you will have added something more like 700 - 800 lbs. For those that tow with one or more full holding tanks, you'd have to add that weight in which case, 1500 - 2000 lbs may not be out of line.