Bedding down (securing) large shower tray

[Qwerty]

On a current job I am working on, I have a large (1400 x 800) shower tray to fit to a totally secure ply base. The tray itself is a fibreglass construction (resin capped). My only concern is that it is a "hollow" type construction (not a solid flat base). There are small ribs built into the fibreglass to stop it from flexing, but I am concerned by the lack of contact it will have with the ply base.

Do I use a cement mortar in regular (dot & dab) in regular places to bed down tray, use a whole load of plasterboard adhesive (in same fashion as cement) that I have left over, or another method?

There is too much of a void really to go using "sticks like *~#+" or gripfill

Thanks, Geoff

 

[Scott]

I put a fibreglass one in my ensuite 4 1/2 years ago. It had a metal frame with 5 feet and i was really dubious about its strength and its movement. Its been totally fine. How deep are the ribs on the bottom? Id solid bed fix it if you can

 

[Qwerty]

Ribs are actually more like feet! They take most of the flex out when it is on the flat surface (I have tested it on the kitchen floor!) There are only 6 little feet, so I am worried that unless I bed it down solid, that it may flex.

Scottley..... what did you fit yours down with?