replacement rear heat pipe (montero2001)

[mitsubishi2001]

My car is limited, it have rear heat system. the steel pipe run the coolant to the back is rusty so bad that it could go any time (according to dealer). I actualy exam it, and it is bad. I plan to install it by myself. anyboy did this job before. please help,
1/ I need to rain the antifreeze from the radiator and the exiting in the pipe (do I need to worry anythings else beside this)
2/ it have 4 bracket attach to the pipe, and hold to the boby by 7 screws. I screw need the suspension I can not figure out the loose them be cause no room to get in the space. (please help)

Dealer quote for this job 300 to 350, the part only $100