I have noticed that the top the hopper lid accumulates an oily and light brown coloured deposit from the exiting smoke. This is more prevelant in colder weather as the hot air, smoke and oil laden,condedses on the cold lid even though it is discharged upwards. 

Being a person that likes to keep my things in top shape and looking new, this bothers me.. Cleaning the hopper lid after every 3 to 4 cooks could be made easier by foiling ..  Another reason to keep the hopper lid clean is the cover..I don't want it to get dirty

inside..  Has anyone done this?

No, but it makes perfect sense.

It is a pain in the butt cleaning it, that is a great idea

I use a burgundy Scotch Brite pad once a year.  Works great.

Did you know your hopper lid is reversible?  I reverse mine in the winter so I can load from the front and don't have to go behind into the snowdrift.

 Reversing the lid was the first thing I did, as I would have to move the pit to access the back.. The downside is ,to remove the back panel, the lid has to be removed. Not really a problem as it's a yearly occurrence (major clean up).