I'll be supremely blunt. If you're not a designer, then don't try to do design work.
Those of us that are good at what we do have spent years learning and honing our craft and spent even more time accumulating practical experience.
Now understand where this statement comes from and WHY.
You own a business engaged in the design and installation of signage and vehicle wraps. WHY, oh dear lord WHY, would you want to try and squeak through with no design experience and supply a CLIENT OF YOURS with ANYTHING that is sub par?
Also think of it from the clients perspective. They are paying good money for what amounts to branding their business...if you were in their shoes, would you want the bare minimum?
I know they all can't be winners, but every sign that leaves your shop, and every wrap that rolls out of your install bay is a reflection on you and your shops capabilities.
If you cannot design, then hire a designer and charge accordingly. Designing isn't just throwing info down on a canvas and arranging it so it fits. Utilizing professionals that know what they are doing is more efficient and makes you and your business look better. Trying to squeak by without the proper knowledge of design or the ability to implement it is a disservice to your clients and your business.