RP from BHB

for 42' feet of fabric you will probably need more dye. 1 bottle of RIT dye is supposed to dye 6 yards of fabric, so you should use about 4.5 bottles. The ratio of dye to water is 1 bottle to 6 gallons of water, so you should have 27 gallons of water. you may want to dye it in sections to make it more manageable, but then you will have seams in your runner.

I think I remember you saying you were going to dye it purple, the RIT website reccomennds that you use double the amount of dye concentrate for purple and other dark colors.

Seams sewn at an angle are much less noticible than blunt seams - i'll draw a picture - to sew an angle seam butt the two piece of fabric perpendicular to each other and sew corner to corner,

here's a Here's a link to the RIT site with some info

HTH! Good luck I can't wait to see pictures!