Post-Script: My interest in pneumatic structures seems to have been an off-shoot of interest in lighter-than-air flight. Two books of note captivated my interest at that time, those being Tensile Structures by Frei Otto and Pneumatic Structures by Thomas Herzog.
The modification I performed to my Seal-a-Meal device was to cut away a portion of the raised lip along the right hand side, originally intended as a guide for positioning the plastic food storage bags, thus permitting one continuous sheet of plastic to be fed through the device uninterrupted.
Lacking a Seal-a-Meal device, a low-wattage soldering iron with flat tip can serve very well for welding plastic film.
A cover sheet of thin tracing paper is placed over the sandwich of plastic film, then a metal straight-edge is used as a guide.
Through experimentation you will find the optimal speed at which to move the iron, using the markings on the straight-edge as a guide, making for a professional looking seam, great for also making curved seams required of balloon envelop gores, for instance.
Type-cast via Remington Quiet-Riter, photos via Lumix G5.