Six years ago I made up a set of sails for my 1/6 scale Silhouette II using ripstop nylon.
It is definitely preferable to keep the weave of the ripstop parallel to the luff.
I used duct tape made by 3M, available in several colours. Black, silver, white, yellow, red, blue... not sure about brown!
I used this to reinforce the "corners" prior to inserting eyelets and also fixing bolt ropes to leech and bottom of mainsail.
Six years on and there is now some sliipping and eyelets have brokn free from head of sails.
I don't consider that a bad life for a set of sails.
A tip if you are fixing bolt ropes:
Prepare your bolt rope adhesive tape by saving some of the peel off backing from something like double sided floor tape
and set out sufficient length of 'tape sticky side up and put two lengths of tape backing down along the length leaving
3x your bolt rope dia gap in the centre. Lay your bolt rope in the gap and roll the tape aroung the rope.
Peeling off one side first and laying the leech or bottom of the sail on that, and getting it all in the right position before
peeling off the other tape, saves an awful lot of cursing and wrongly stuck bits, including your fingers.
It may go without saying but make sure you are working in a dust free environment and wipe the ripstop before sticking.
Nothing ruins adhesive faster than dust. (Well talc will!!)
Good luck