Agree with Les' and 109. If you think that masking is a bit difficult, try this;
Use Tamiya masking tape, and put a length onto a smooth surface, eg, glass, 'Formica' worktop etc. Paint it the colour of the framework and, when dry, cut 'slices' the width required for the canopy framework. Place these in position, rub down with the edge of your fingernail or the back of a blunt blade. When satisfied they stuck down firmly, seal in place with a thin coat of gloss varnish, or Johnson's Klear (Future, in the 'States). If required, carefully paint the 'frame' in matt varnish. Voila! Neat, straight frames!
If you're having problems sizing your pics, take the tip from Wurger etc, download Irfanview, it's free, and dead easy to use. Just select 800 pixels as the first size, and the 'system' does the rest. The size works well, and you can easily re-size again for other applications if you need to.
Terry.