(T.L.) box design help?

Good Morning everyone,

I am looking to do a different type of box for my project. I am looking on building a (T.L.) called a transmission line box for a friend of mine. I have called the following people and no one seems to be able to help me out?

1. Meniscus audio group (Doesn't do this type of service anymore.)

2. Madisound ( Just pointed me to a program.)

3. RedRock acoustics ( Doesn't answer phone after calling so many times and doesn't return my e-mails?

4. Parts express ( Couldn't help me out they have no idea or programs to help me with this type of box I was told.)

I am willing to learn how to figure and make this type of box out. Could someone please point me in the right direction. Programs or a company who could help me out? I feel I am at a loss. Thanks Jd