That stuff is great hey, i bought a roll of it from kmart ( i think ) and have used it in our cars, i cut a small piece for the ashtray which holds all our spare change and i cut a piece for the dash pocket where we keep our phones etc.
I find with campervans especially converted ones that may of had a hard past life is people put so much effort into getting them ready that they forget about the mechanicals, get it serviced and make sure it has all new belts and carry spares for just incase, they dont take up any room and are peace of mind when you lose a belt in the middle of no where that runs your waterpump..
Make sure the radiator is in good condition and put mesh up in front of it to protect it from flying rocks and bugs, trying to find a pin hole leak in a radiator is not fun. I've seen alot of people running shade cloth to protect there radiators but i dont think it lets enough air through to keep the car cool, you can get wire fly screen that would do a better job and reinforce it with a small frame.
This stuff is really easy to think of, basically think of every car you have ever seen pulled over on the side of a freeway or highway with its bonnet up or with a flat tyre and you will soon realise what you should be focusing on.
I wont go into any more high detail but here are afew more pointers.
* Spare tyres - they should be easy to get to so you dont have to unpack all your gear to get one out, depending on the trip i would even carry 2. Make sure you have a working jack and wheel brace too.
* Air compressor - The type that inflates tyres etc, you will rarely use this but even if you get a flat and have to pull over and inflate the tyre every few km till you get to the nearest town it will be worth having one on board. You can use it to blow the red dust out of the van too.
* A healthy battery - Self explanatory, but keep a set of jumper leads on board just incase, it may not be you who has to use them but you could help out a fellow camper in need if you have them.
There are heaps of others.. but i'll be quiet for now lol