Here's my Hulkbuster MOC, wanted to make it as accurate as possible while keeping the scale. Yes you can fit an Iron Man Minifigure inside very easily : r/lego
LEGO Hulkbuster MOC by moxi (chest open + minifig) | Flickr
LEGO MOC Hulkbuster 76247x2 by anderson_brick_art | Rebrickable - Build with LEGO
LEGO MOC Chubbybot's Iron Man Hulkbuster by Rick222 | Rebrickable - Build with LEGO