there is no such thing as easy with that box. easiest is remove the entire dash assembly.
otherwise working around it. you have vacuum lines that must be disconnected. the heater core hoses in the engine bay have to be disconnected. the A/C freon has to be drained and the hoses and expansion valve have to be removed.
from inside the car, glovebox insert and i would remove the glovebox door to gain access.
there is a dash board support bracket that has to come out. the accessories panel that is above the glovebox has to come out, unplugging all the wires.
i think i had to pop the dash top and remove the passenger side vent tube that goes to the air vent.
then there are electrical connectors on the box.
1 screw up by the fresh air intake hat.
then 2 or 3 nuts you have to access in the engine bay.
remove the passenger Seat!
you then play the worst game of tetris Ever trying to get the box out with out breaking it because the fiberglass is brittle.
once the thing is out you have to rebuilt it clean it out hope nothing else is broken then reassemble and then reinstall it.
http://s1031.photobucket.com/user/72hcode/library/Heater%20Box%20AC?sort=2&page=1
i spent a couple of weeks getting mine out, fixed and in.
also when you do this you find out how bad the rust is on your cowl.... usually you cry a lot.
if you can get your hands around the drain you might be able to patch it, you will need to pull the seats out and i would pull the carpets out to get access, then you could wrap the drain with repair cloth and mix up resin to try and stabilize the crack. or black duct tape that sucker back on and never talk about it again
