As mentioned elsewhere in this thread I have had the "help" of a spray painter on bits of the build, which has been a mixed experience. I think in this case it was totally unnecessary but he just wanted to further 'prove his abilities' to me. At least it means a little less filler though!
It was not particularly hard, you just need to be gentle with the heat. I think with how much modern fillers have progressed, for some applications it can just be a waste of time.