I have been pondering this question for some time and wandering around the internet found "Aquatecnic Waterproofing Solutions" www.wetroom.info who produce a waterproofing system for wetrooms (shower areas to thee and me). They sent me a pack containing technical details and samples. About £117 to do the shower enclosere end floor- to me, money well spent for piece of mind. I dont want to spend half my retirement re-tiling!
Try "Granofix"tile adhesive manufacturer, lots of data sheets on the web and helpful on the phone. They produce flexible adhesives and grouts. If silicone was the best they wouldn't be in business!
If you want quality adhesives/sealants speak to ARBO. Many caravans are held together with their products and very few physical fasteners.
Dont cut corners - they eventually fall off.