Hi folks,

I'm a UK based hobbyist about to embark on a composite project that I need to do some learning about and probably get some guidance for!  I've made a few things using composites in the past from glass/polyester windsurfing skegs in the 1980s through to the most recent where I vacuum skinned a polystyrene computer monitor protective packaging box insert with a carbon/aramid weave epoxy matrix to make a flight case as part of my vacuum learning.  

Anyway my big project is to build an overlanding expedition camper habitation unit to go on the back of my Unimog.  This will be a 4.2m x 2.1m x 2.1m monocoque structure made from laminated panels.  I want to build it myself as the built units are all glass/polyester based and made from panels glued into extruded corner profiles.  I hope to be able to build a lighter structure of equal strength by using better materials and by creating a continuous matrix monocoque.  Weight is important as reducing the unit weight either gives you more carrying capacity for fuel/water/junk for long off grid trips or it allows for safer travel on challenging terrain with things like timber bridges or unconsolidated surfaces.  

Having said that everything is relative.  The chassis is 4.5 tonnes and even with some things like composite roof, doors bonnet etc which I might upgrade in time it's still a bit of a beast!  The habitation unit will have a target wet weight of 2.5 tonnes (including all components fixtures etc).  I have yet to work out what that translates to in terms of dry box target weight.  

Whilst I haven't used it for a while, I have an aero engineering degree and 30 years ago studied aerostructures and materials science as a result so I can grasp design concepts.  My maths is probably no longer strong enough to do highly complex load distribution calculations but I'm hoping that I will polish this up enough to get by.  I have thought about the basic design principles and have reached the following conclusions:

• Basic structure will be based on vacuum formed aramid/carbon/PU foam/carbon/timber veneer laminate epoxy matrix panels.  This is for: impact resistance/structural strength/thermal insulation/structural strength/aesthetics.
• Panels will made up of carbon wrapped sections to create a series of "cross beams" within each panel for transverse strength enhancement.  
• Assembly pattern will be to create sections, combine sections into panels, combine panels into the overall box.  
• I will need a big (5m x 3m) flat plane surface to do everything on to get adequate surface finish - I'm hoping that I can use the newly skimmed concrete floor of an industrial unit I have access to for this.  

Anyway, key thing now is to work out now are what weight of fabrics I need to give me the load capacity I need - any guidance of where to look gratefully received!

All the best

Nathan