Hi. I am replacing at shower tray with a 800 x 800 quadrant shower tray. Unable to use riser legs due to space I have to fit it into is very tight for space. I have made a plinth for it to sit on. All surounding edges are suported. Question is, the inside of tray is about 5mm higher than the edges. Does this need to have any support under it. There was no space for a riser leg in the middle of the tray So I take it it should be strong enough with out any extra support. Is it ok just to support edges. It it strong enough.