baggin a fs and a dually

is it hard? i know it pretty much can come as a kit, but what kind of cutting is involveded besides notching the back. i want a fs truck but aint made up my mind about a dually or not. whats the difference baggin the two? and this is gonna be a tow pig, will i still be able to tow my mazda with it bagged? i want to buy one and leave it stock but i know i never will be able to do that.