I've done mucho welding in these type situations. You have little to worry about from gas fumes. If you small gas, don't weld. Otherwise, proceed with due caution. Welding fumes cause Parkinson's disease so adequate ventilation is a must. My main concern would be personal injury from overhead welding. I always have an air hose handy when welding, to blow out little paint fires at the hot spot. Find something you can fan out little flames with and never assume that the backside is not on fire after you zap a weld. Always check immediately. Backward ball cap to keep slag out of the back of your shirt, leather top shoes, etc.
