Franke wash trough

I purchased two wash troughs. Both rusted within a year. When I asked for a replacement for the one that was just out of the warranty period I was refused and asked to use innox rust cream, which i did. However it's now rusted through and developed a leak. It's been 2 yrs nw and I find myself in the position where I need to replace an item which I expected to last a good long time. Consider the cost implications as well as the inconvenience. I'm not finding anything which has the dimensions I require. Very disappointing. N.B this the econo wash trough and I was told that it shouldn't be used along the coast. I wasn't made aware of that when purchasing and why then is it being sold along the coast? Set you up for failure. The assistant suggested that the rust occurred due to the usage of soap. Was I not supposed to use soap to wash in the wash trough then? My bad.