Hutch:

There's another solution:
- insert a doorframe of the required size; give it a colour or a texture
- inside the doorframe, insert a box of the correct size
- choose Modify -> Texture , choose the texture of your liking, but do NOT apply it
- choose Modify and give the texture the exact height of the box that you inserted inside the doorframe

If all is well, you should now see a texture that repeats exactly once (vertically). If the width of the texture isn't correct, you will have to use a graphics program to change the size of the texture to exactly match the size of the inserted box.

I hope I explained it clearly enough.
Good luck.

Hans