Some nice idea coming out Guy's thanks very much.
Keith if your looking for somthing like the boot storage in the link you posted, I have a freind / neighbour who refits & builds some very tasty looking interiours for VW Campers, I'm sure he could knock somthing like that up for you at a sensible price. If you'd like he's contact number just drop me a PM.
Megafronty, that's a great idea. Perhaps we could try and sort out getting you an late A & B series Frontys for an hour or two and you can see if it's viable to make off the shelf kits.
Barrie (Mr Mud) there was a guy on here, think his Forum name was Wizardovoz (or somthing similar) that made tubular manifolds. Think he was based over Oxford way. Might be worth a quick search if your after one ?
Think the re-ocurring ones seem to be snorkels, bumpers & roof racks.
With regard to snorkels, how about a single peice of stainless steel tube that's been mandrel bent that will simply slide through a hole in the wing and secure to the A-post and inner wing, with the obligitory bit of flexi from the end of the pipe to the air box ?
As for Bumpers, what type do people actually want ? Do you want to pay the £250 - £350 for a full size winch bumper like Trugga's or the one on my old B series or would you prefer to see somthing cheaper made out of Tube, a bit like the ones normally seen on Landrover Defender's, etc?
Now with roof racks, strong & light weight arn't things that go easily hand in hand without using more expensive materials like Aluminium & Titanium. Would people be willing to pay more for somthing that is top spec or do you just want somthing that's heavy duty, will take a spare wheel, a jerry can and a bit of lugage, etc and only want to spend a couple of hundred quid ?????
As for maunfacturing diff lockers, it's a really nice idea but to be honest it would be cost prohibitive.

It takes a lot of money to set up tooling for an initial production run on somthing like that and for the low quantity's that your likely to sell, sadly it just wouldn't be worth it, or at least not if production where to kept in the UK anyway......