Good question. I've never tried the hairspray method. I did try acrylic paints over a coat of future over a coat of metal but the paint tore more than chipped. I'm inclined to try the Micro Mask-on-a-sponge method combined with some hand work.
Spent a good bit of time hacking at this beast with my Dremel and drill. The base was pretty heavy so I drilled a bunch of lightening holes while at the same time opening up the front ladder entry spots. You can see the blue markings where I still need to shave it all down to make room for the internal levels buildup.
I also used a cutting bit to open up the roto-cast pieces (there are some THICK spots!) and removed the front door. I also hollowed out one of the side entry ramp sections.
Wow ! What a fantastic build . The Sandcrawler has always been one of my favourite Star Wars craft and I've always harboured plans to build one . Can't wait to see her with some paint on . Keep up the good work . ;D