oven insufficiency alert

I was just avoiding work (again)--er, taking a little break--and reading this yummy brownie recipe EvilChefMom just posted and remembered:

My (rental) oven doesn't maintain temperature at all! I finally bought an oven thermometer which lead me to discovery #1: My oven runs 35-50 degrees cool.

Then! Two days ago, while baking my scones for the Strawberry Shortcake, I discovered (#2) that after 30 minutes of preheating at 450^o, the oven was still hovering around 345^o.

What to do? Anyone have any suggestions about helping my oven attain high heat? Besides moving, which is kind of in the works; or perhaps wrapping my oven in industrial-strength foil?