Sealing the ribs with a heat gun sure it can be done with a glove to apply momentary pressure directly on the rib which is an acquired skil and the reason I reccomended for the beginner to use the iron to accomplish this with perfect up and down applications of pressure with no movement of the material in any direction and this only after the complete shrinking has already been done.

Failure to seal all the surfaces including the ribs in a lightly built trainer wing (and specifically those such as the Kaydet Senior and LT-40) Will result in a wing severely impaired in torsional stiffness and gentlemen that means dangerous.

"Some do and some Don't " indeed well we are not talking about giant scales here or as another put it an astro hog, that airplane has a wing built like a diving board, Definately not a trainer.

This is the trainer forum and from the OP's questions and statements he seems to be a newbie very likely the airplane in question is a typical trainer with very little structural 'D' tube sheeting and a dangerous one if only sealed on the outside perimeter. To trivialise the need for rib sealing on the typical trainer to the new fellows does them a disservice.

Thats only my opinion as always and I am an expert in nothing what I am is a survivor.