I sew quite a lot, but to actually describe how to make them is not easy, because its just like making ordinary curtains except the heading tape is different and that's all, so perhaps the editor would like to run an article on how to make them with illustrations and instructions in the magazine. The main thing however is to choose the material carefully for thickness and pattern, caravan windows are small and if the material is too thick they will look too bulky, if the material is too thin they will look feeble and if the pattern is too big they will look out of place, likewise if it is too small they will look too busy. Try and get the material as close in texture and pattern to what's there already. Dark colours will show up fade marks quickly, so lighter colours are best. Measure the finished size of the curtain by lenghth and add 2" for the top hem (because you don't want a load of bulk on the header tape) and about 3" for the bottom hem. Measure the existing width of the replacement curtain - this will be the width of material needed, so if the fabric is wide cut it down, allowing 0.5" either side for the side hems. Do the same for the lining but make the lining dimension 1" shorter in the length. Hem both the curtain fabric and lining fabric, turning the hems to 1.5" twice, press with an iron, then turn them inside out and attach them together down the sides making sure that the tops line up. Turn them to the right side and press out the sides, then turn the top over by 1" press, turn over again 1" and pin the heading tape tightly to the top. Sew the tape to the top and finally press. Good luck and perhaps the succesful ones could send photos into the magazine to go with the article!!
Sian
PS for pelmets that are frilled double the fabric width to get the frill, for pelmets that are just covered use a staple gun and for the totally co-ordinated look get the cushion covers made up locally, most towns have soft furnishing businesses that will run them up at a reasonable cost.