I have my frig removed also. One produce that you may want is Rust Fighter
1.This is a 3M produce that is sold at auto body supply shops. It is a
spray with a long nozzel like the carb cleaner cans, but longer. $18/large
can. It never drys, and will reshape itself and flow to fit into any
crevices. It will displace water and seal out corosion.

In my vanagon, I have removed the insulation directly behind the frig. I
get too much interior heat from the frig and believe that the bare steel
wall will conduct some of this heat out through the van wall.About 3.5 sq
ft of area here.If,in summer the outside air temp is over about 95 degrees,
I will put a "rubber"magnetic sign type cover on the outside area over
where the frig is. This cover is the type that is used for advertising.
About 1.5 ft X 2.5 ft X very thin w/ a bit of foam insulation under it.This
will keep the direct sun from heating the rear frig area up in day time. At
nite it is removed for cooling. The fan is set to come on at 140 degrees
and go off at 120, so the average temp probably about 130 degrees. This,if
your fan comes on regularly. Outside is cool now , so I wont be able to
tell if this makes much difference till summer.I think it will cool things
down behind there. Every little bit helps.