Sounds like a great way to trap salt laden moisture next to the steel to promote corrosion from inside!

 

looks very nice.i live in the rust belt in OHIO,USA.i've rebult alot of cars and pickups,and what i do upon completion is to flood rocker panels with rustolium paint.i level car, remove step plates,drill 1 1/2" or so hole, elevate car,plug all drain holes with tape or dum-dum[clay like putty],fill rocker up with paint,let stand for 20 minutes, jack up front end install cardboard trough so it can drain back into cans and pull putty out of rear.as most has drained out i remove the rest so as to get good drainage.use plastic gloves.i also flood above rear 1/4 panels and paint inside lower doors 6"s.i've cut into old rustproofed rocker panels and have found that it has curled away and no longer works whereas rustolium sticks to eveything even light dirt...steve