Thanks all for your comments.
I'm still undecided, as we like to have every thing in the trailer, ready to go. Therefore I'm keen on making the trailer the width of the bed base, with internal tubs (I've noticed on this forum what you guys call a tub, and what a tub is to me, is way different. I think of tubs as somewhere to house a wheel, and not the box of a trailer).
The bloke that we'll use for the canvas, showed me some photos of camper tents that he has done, with the soft floor not fixed to the bed base, but following the shape of the bottom of the trailer, around the guard, then back down the bottom of the trailer. This exposed the side boxes of this particular trailer, to the inside of the tent. I thought this was a pearler of an idea, as it gives Pony, (my Wife) some where to lock her 9 handbags, 34 cameras, phone etc, all inside the tent. (OK, in all seriousness, she doesn't have that much crap, but it would be handy to have a lockable box, inside the tent).
But.....I don't think I need them on the other side. Can you have boxes on one side and not the other? That would be like shaving one eyebrow and not the other, yes?
Do side boxes leak? Do they fill up with dust, water, mud, sand etc? Are they any good for storing cameras and stuff, or are they like the boot of an old Kingswood?
I'm loving the idea, but are they practical?
Shane.