Broadly speaking, I think it partly depends on how well you maintain the TT while you own it. If someone inspects the roof every 2-3 years and adds sealant to the seams as necessary, it could last many years. Keep it under cover while not in use to avoid UV and weather exposure, and it might last 2-3 decades. You are correct that rough roads will loosen things more quickly, but I wouldn't expect welds to break for the first 10-15 years on most any TT. Sorry I can't speak directly to the brand and model durability.