This was something I had saved awhile ago from another post. Hope you can use it!
I don't think there is a pattern, since all you are dealing with are big rectangles, made to the length and width of your window (it doesn't hurt to be a little generous with width). Generally they are pinch pleated at the top, sometimes at the bottom. Use curtain buckram to stiffen and make these pleats stand nicely. The biggest issue will be the hardware in your trailer--there are so many different kinds. In my (61), it had snaps--and I had a dickens of a time finding snap tape that fit the snaps on the carrier pieces. Since I had to hand sew in these snap tapes, using the nice pleater tape and hooks was not possible--I sewed in the pleats.
Here is my process:
Measure window space, divide width in half and calculate fabric requirements, considering 5.5" every 4" for pleats, 4.5" at top and bottom for top seam allowance and bottom hem, and 2" extra edge allowance on the sides for edges. Also--extra fabric has to be added if you have to seam two pieces together to get the width you want.
Heck, I'm on lunch break...Here are directions for top pleated curtains:
This works out as:
Fabric Width (per panel)
(Width of window/2)/4=Y
Y*5.5=extra fabric width for pleats.
Total Fabic Width=Width of Window + Extra Fabric width for pleats + 2" edge allowance (+ 1" seam allowance if sewing two pieces of fabric together to get sufficient width for the panel)
Length of window +4.5" + any desired overhang
Step 1. Cut curtain fabric and lining to the same dimensions, except make the lining 1/2" shorter in length. Seam sides if necessary to get desired width.
Step 2. Lay the fabric down with the pretty side of the curtain fabric lying up. Put the lining fabric on top of it, so that the coated side faces up as well. Then unroll and place 4" curtain buckram at the top edge. Pin at the top. Seam the top edge. Fold the fashion fabric over the seam allowance (so it goes up and over the buckram and lining fabrics). Press.
Step 3. Measure the length and mark the desired hem point on both fashion and lining fabric (lining should be 1/4" shorter). Fold hems and stitch in place.
Step 4. Pin pleats in place. This is easiest started from the center--if you have an odd number of pleat bunches, then the center pleat is there, if even, measure 2" from the center point. Each bunch is 3 pleats. Hint--place pleats on both panels at the same time, so you can make them match. Press pleats in place.
Step 5. Sew bar tacks 4" from the top on each pleat set to hold in place. Hand tack the backs of pleats in place at the top of the curtain (this is a fine detail I'll probably have to photograph later for it to make sense, but it make it look much crisper). Attach carrier mechanism appropriate to your trailer.
Step 6. Test in trailer. Decide if you want to cut edges. Sew edges closed.
Ones with bottom and top pleats are almost the same, except you will sew the curtain and lining fabrics into a big tube, inserting top and bottom lengths of curtain buckram. Then do pleats at the top and bottom at the same time so they match.