A good friend of mine, K5URU, developed this mobile mast with his dad recently. I just had to post this here for him because I’ve never seen such a sweet mast!
Check out the following article (.pdf): K5URU Mobile Mast
I have a keen interest in eventually going HF mobile one day, but that project is for another day!
This is a well built mast that may help spark some ideas of your own.