Unless you have changed your designs from the ones that you asked me to draw up for you then you might be pleased to hear that the surface area of your hull is 4.3sqm.
To be honest no-one really refers to modern rotmomoulded boats as tupperware boats anymore, rotomoulding has come on along way in recent years. Most mass produced dinghies are made this way. The computer controlled molds can do some amazing things such as creating much lighter stiffer boats by using foamed polyethylene between solid skins. They can form thicker sections locally and contain stiffening members. Although they won't be as light as ply or GRP sandwich they are much better than you are making out.
Most holiday companies and rental companies won't entertain the idea of a boat made from any other process. This "feeling the hull wobble underneath you" is just nonsense.
