The factory shades in our 21 are very light and don't block ambient or park lighting very well for sleeping so my wife made some blackout curtains. They work very well to keep the trailer dark for sleeping. If you want to make a set for yourself see the steps below.
light blocking fabric, measure as required
1 1/2 wide X 1/8 thick steel bar, available in 36 inch lengths at Home Depot for $6.40
7/8 inch wide X 1 7/8 long X 3/8 thick magnets item # 07044 at Home Depot for $2.98/pair
1 inch long ring shank panelboard nails available at Home Depot (comes in a pack)
Permatex rust treatment, available at NAPA auto supply
1) unscrew and remove the window valances, save screws.
2) measure the valance length and window height and buy light blocking fabric, include excess for hems and magnet pockets.
3) cut the steel bar into 1 X 2 plates, photo 1. Two for each valance.
4) drill and countersink 2 nail holes in steel plates, file edges smooth, photo 1.
5) clean/degrease then coat the steel with permatex rust treatment, this prevents the steel from rusting.
Step 6 & 7 are done together. Pilot one hole and nail, then pilot the second hole and nail.
6) use the drilled plate to locate and drill 1/16 pilot holes 1 inch deep in the valance ends to prevent splitting the wood.
7) nail the steel plates to the valance ends, photo 2.
8) measure the fabric allowing for the hem and magnet pockets and cut to size. Note the magnet pockets are on the back side.
9) sew hems and pockets, make the pockets tight so the magnets won't slip out, photos 4 and 5. Practice on a piece of scrap first.
10) reattach valances with screws.
11) now it's ready to attach the curtain to the valance.
If the magnet pockets are too difficult to sew an alternate process may be to make magnet pockets separately and then sew them onto the curtain after hemming. Velcro might work but I think the magnets are easier to use. I had a couple more photos but could only attach 4.