What type of board to reinforce existing wooden floor in cabin

[RocketScienceSmurf]

I am renovating a cabin and have started to look over the floor in the section that will become a bathroom and will also house a 500-liter slingtank plus a freshwater tank. It seems to be double-layered tongue-and-groove planks under the masonite and the frame marked with thicker lines on the sketch are heavy joists supporting everything.

The electric boiler/slingtank will likely weigh close to 700kg when filled. Should it be sufficient to reinforce with 22mm chipboard on top of the existing floor, or should I consider another solution and, if I lay chipboard before the other sheets (50mm grooved polystyrene for underfloor heating is to be laid in part of the room), where should the vapor barrier be placed?

 

[fribygg]

I would probably cast or mason some plinth to take the large (700kg) point load.

 

[heimlaga]

Chipboard flooring reinforces nothing. There must be a proper foundation underneath or strong beams.

 

[RocketScienceSmurf]

It's mostly about trying to distribute the weight as best as possible. The pan is 70x70.

It is a cabin on stilts, so casting does not seem like a reasonable option to me.

 

[fribygg]

It's a cabin on piers, so casting doesn't seem like a reasonable option to me.

Then use masonry, concrete blocks bear weight well.