There are a few portions of the Mk4 frame (mainly the trunk/fuel tank area) that appear the internal portion of the steel tube is exposed (not welded into another support structure but left open). Is there any need to seal these off so humidity doesn't get into the frame tubes? Between 1) my high humidity summers and potential for road salts in the winter, and 2) my compulsion to protect every inch of exposed steel, I'm trying to get a handle on what is necessary and what is overkill.