mig welding

I've never had an issue like that before pop up.........BUT, I would just buy a cheap piece of plastic sheeting from Home Depot......cut it big enough to make a little "tent"....tape it to the dash and rear deck, and weld under it using a little prop rod to hold it up off your head....it won't hit the headliner for sure.

Usually, if you use MIG (NOT flux core) , you'll have very little slag and sparking issues.