Protection of back of paper/canvas

Usually when Marvelseal is used, it is as part of a microclimate package – including glazing and a barrier material with molecular sieves (i.e. MicroChamber paper) to help remove pollutants from the microclimate.  In a sealed package, the object, mat board/backing materials, and glazing (the glass or acrylic) are joined together as a single unit and sealed along the edges. This provides a safe environment—a microclimate—for an object, protecting it from changing humidity, dust, and pests. The sealed package can be used as storage housing or tucked into a picture frame for display. A framed sealed package looks no different from traditional picture framing, but provides a higher level of protection for the object. 
The link you’ve provided has instructions for adding a sort of waterproof backing to the paper, but that’s it.  I’d also caution against ironing plastic bags or anything else to your piece, as this can be quite permanent and there are often proprietary additives in the plastic bags you get at the supermarket (for example, dyes) which can unleash all kinds of horror on your art.  I’d avoid doing this for paper.

This article has a bit more information on creating a microclimate package:  http://www.pictureframingmagazine.net/portals/0/pfm/pdfs/2014/Feb_14_Mounting.pdf

​Also, just to add – good fine art framers can often carry out this service for you, so if constructing a sealed package is of interest this may be something to look into!

​I am sorry that I missed this. I have thought about using a heat sealing foil on back of paper, before and have always come back to the idea of why does it have to be attached? One can interleave or loose line the back of the paper with any heat sealing foil or Corrosion Intercept and get plenty of barrier protection, without worrying about driving volatiles from the plastic into the paper with heat. Having tested this out frequently, I can assure you that the polyethylene will  not bond well to sized water color paper, while it will bond well to a fiberous tissue, which I why I have recommended using Univ. Prod, 12 gram unbuffered tissue, heat bonded to Volara, to make spacers to go with paper and photo, since so many conservators in those media are wary of Volara touching paper or photos. As to the wisdom of keeping pollutants from the back of the art, I am all for it, but using aluminum foil per se, is less wise than using a commercial foil, since the aluminum will oxidize and stain, so it is better to have encased, between plastic layers. Yes, I think loose lining the back of canvases is a great idea, with the polyester side toward the canvas, since the polyethylene can contain slip agents.
Hugh Phibbs