I did this DIY out of simple frustation of wanting some coverage without always wearing a camisole. Also, due to not being able to find a tube top that stays up without squeezing the daylights out of my "girls".
I thoroughly don't like this "camisole under a spaghetti strap dress" look.
Start with a plain, well fitting camisole.
Try it on upside down and make a mark as to how long you want it. I kept mine about 2" below my chest.
Use a ruler or tape measure and mark from the bottom up the same length as your original mark.
Cut along your marked line.
Make your cut all the way through. Now you have a tube top! Wear the hem side at the top. You can still use the actual top as a shorter camisole.
This makes for some coverage in the front without all the extra straps, and the "hey, I'm wearing a camisole" look.
Now you have a camisole free back while still having coverage in the front.