polystyrene blocks where in perth

Hi sub

For marine ply try Cullitys balcatta

Sorry cant help with foam

chers

If you go to Ewing, Radium or Mills St in Welshpool (I've forgotten which one) there is a mob who deal in coolroom panels. They often have FREE foam sheets on the verge from panels that have delaminated. Thickness is usually 50, 75 and occasionally 100mm.
They are on the LHS when travelling from Welshpool Rd towards the railway line.

Hi
A couple of years ago I purchased polystyrene foam (normal building variety) and used it as a float in a hydroponics setup. It slowly absorbed water and once saturated I couldn’t get it out. I then purchase more foam and had success sealing the foam with an expensive paint-on waterproof membrane. If you want the open cell foam they use for cool rooms and building panels – Clarke Rubber sell it. If it was for a safety device I would try and find the closed cell product.

Why not use pouring foam as boat manufacturers do?

Yep, the high density stuff is double the price. I bought some sheets from Foamsales in Balcatta. They probably sell larger blocks but I didn't see any at the time. I got the higher density styrofoam to act as an insulating backing to some van wall panels I installed.