My First (Stupid) Question

I am an absolute rank amateur with no previous experience other than a few GF/GRP Moulds at school (a long time ago).

In Order to keep my question simple I wont go into the detail of what I am trying to do but the closest thing I can suggest is if I wanted to build a CF caravan (yes the thing you tow) and I get that I can buy some flat sheets of sandwich and stick them together and end up with a very square caravan but I am thinking a bit more adventurously than that.

So here goes... I would like to build a caravan and I assume (but ask the question anyway) is it practical to build a BIG box using vacuum induction forming techniques or do I have to create it in sections and I have a fairly good understanding of bonding and area vs. strength and concepts like tensile strength and stressed members, but what I don't get is where I start. For example do I plan to build a nose-cone and tail then fill the middle in with square flat sheets?

If I go down that route how do i get the right strength / cost ratio and on a practical note - how do I fit doors and windows?

I also assume I'd need a big thick sandwich construction floor and am thinking about honeycomb but I don't seem to be able to find anything that tells me how to construct a section of rigid panel using the honeycomb.

Any thoughts?

PS I appreciate this size/scale isn't something a beginner should be having a go at, but it's the only thing I'm interested in building at the moment!

PPS - just watched the video of the indian guys building a 42ft boat in one go so it must be do-able if very complicated!