the people in the garage tell me i should get my van waxoyl'd underneath. i've heard mixed reports of its efficacy. anybody had this done/done it to their vehicle and can put me right?

Just had my Land Rover done by Rustmaster. They use some new fangled stuff that supposedly is more flexible than the last so it can stay in place while the metal heats up and cools down, unlike the old stuff which seemed to crack and let water in behind it. There are reports for and against Waxoyl all over the net, and loads of other people will swear by a myriad of other products. But it seems popular with Land Rover owners and a lot of those vehicles get a far harder time than I suspect your van does.

Rustmaster did a good job too – not cheap, but thorough and they let you watch to make sure you're happy it's all been done. Price includes cavity waxing for doors and bits where you wouldn't want/couldn't get waxoyl.

In all honesty, unless your vehicles bodywork is galvanised or aluminium then you are wasting your time. The corrosion will have started the moment the car left the production line and the waxoyl will just sit on top. It may slow down the evidence of it for a bit but the final outcome will be the same. Most decent new vehicles are galvanised and if yours is one then it's as protected as it can be.