Hmmm, I have to admit I am re-thinking my strategy. I visited the local Bunnings on the weekend to get some sizes and such of certain materials, but didn't get any further.
Like I said, I have a laundry tub for drainage and washing. The main reason behind the sink was as a tempering bath and to control splashes. I have been using trays on benches for ages and I think I have only had to temper outside of my Jobo once. This is going to possibly become a bit of a luxury and maybe not really required.
I think I might go back making a simple bench top. This will also give me additional flexibility, so larger trays don't necessarily need to 'fit'.