One of the advantages for me in the roller method (apart from the cost!), is that if the van does get a prang or a scratch or rust spot, I won't be devastated about damage - I can simply get the sander and roller out and it'll be as good as new.
I had quite a few cynical neighbours passing comment when they saw me overalled up ready to start work at the weekend, I must admit even the most cynical was suitably impressed with the results.

Silky