You can do a floating deck and is really your only option.
Floating roof double deck.
Floating roof atmospheric storage tanks.
In the same sealing condition compared with external floating roof tank internal floating roof tank can further reduce the volatilization loss as a result of that compared with double deck floating roof on external floating roof tank shaded by fixed roof and the gas phase layer between fixed roof and internal floating plate have a more significant effect on heat insulation.
However i would highly recommend that you consider a that the epdm is lying flat on the roof subfloor without any sharp objects that can puncture the edpm once sleepers are laid over top and placed under load.
In my humble opinion the double deck arrangement would be a more robust design but may cost extra and a detailed techno economic evaluation would be needed to arrive at the optimum option.
The outer ring of the compartments is the main liquid tight buoyancy for the roof.
I m not surprised that steel floating roofs change shape when they are floated or when their temperature changes rapidly.
It consists of an open topped cylindrical steel shell equipped with a roof that floats on the surface of the stored liquid.
External floating roof tank double deck type an external floating roof tank is a storage tank commonly used to store large quantities of petroleum products such as crude oil or condensate.
You can use 2x material laid flat or 4x material also as sleepers.
Sketches are provided in the article depicting the pan type pontoon and double deck arrangement for external floating roof tanks.
These include new builds together with the evaluation of existing roof designs for suitability such as analysing the various flotation cases and repair.
The low single deck is the more efficient of the two for 30 to 170 foot diameter tanks.
The two preferred configurations for external floating roofs are the double deck and the low single deck with 30 minimum pontoon area.
Over the years jm dixon associates has undertaken the design of many floating roofs both double and single deck for world renowned clients such as philips 66 exxon mobil and ineos.
Double deck roof is much heavier than single deck one hence it is more rigid.
The sketches shown illustrate the above single deck and double deck floating roof with the critical components for these structures.
Different roof configurations were shown in figure 100 1.