: What do you call them and where do you get them?:

Ratchet straps will work just great here, John. All the big box stores around here (Home Depot, Lowe's) and most of the Aces and True Values have them, in packages of 4 for $15-20. Look either in the fastener section or the hand tool section. Make sure you get the ratchets and not the cheaper cam clamps; the ratchets give finer control over clamping pressure, and are far more positive in operation. I used 8 of them to put my Guillemot together, no spreaders, no tape, and it cinched up just fine. You can insert wedges under the straps over any high spots and coax things into proper alignment, all from the outside of the boat. A rubber mallet is a useful tool also.

BTW, did you hot-glue your inner seam tape in place first? A little dab every 6"-8" will greatly simplify your life in the short term.