I don't mind foiling my pan. I bought a huge roll of 18" Heavy Duty foil at Sam's. So, it is cheaper than the foil pans although if you buy them at Sam's/Costco they are pretty cheap too.
My only worry would be if the foil lip on the pan that slides into the guides would hold up if you got the pan pretty full. I have had my pan near overflowing a couple of times and I am guessing that the foil lip would have given way. That was with a full 5 trays of very moist pepper stix. So, for most traditional smokes that don't give off that my drippings it may work just fine.
Good thinking though. I am always looking for new ideas like this. Thanks for sharing.