I am just finishing painting mine in Cellulose. I bought it from Buzzweld in Bristol, (they do mail order). They were significantly cheaper than my preferred supplier (Craftmaster) but the pennies are rapidly running out! The white paint was great, but I had some trouble with the blue paint, (the dark blue pigment wouldn't mix in properly) but they couriered out a replacement tin pretty sharpish with no problems, which was perfect.
Cellulose is great for DIY and very easy to rectify any runs or problems afterwards. If you aren't sure what is already on the van, hold a cloth soaked in cellulose thinners against if for a few seconds and see if you get a reaction, if not you are good to go. If there is a reaction you can either strip the lot off, or give it a couple of coats of barcoat sealer first. Cellulose paint naturally sprays slightly matt, (although I lay on a well-thinned final coat to gloss it up). You then colour sand, cut and polish for full gloss, but you could leave out some of these steps if you want to keep it looking less glossy. Look forward to hearing how you get on!