AHi, I am making a large sculpture out of rice crispy treats and air brushing it but was wondering what would be the best to cover it with? Modelling chocolate, gumpaste or fondant? Thanks :)

eliminate gumpaste--either of the remaining or a combination of those two--

I cover all of my rice krispie figures with candy melts first, like 2 coats and and i basically use the warmth of my hands to smooth is out as best i can.  Then i spray it with water or use a little piping gel and cover with fondant.  hope that helps.

Depends on how much detail you are going to add. I find I get better detail with MC, but I use fondant when I don't need as much cause it is more cost effective. Like Rooch I also coat the RKT with warm candy melts as a first coat.