Engineering firms can be hesitant to use contractors and I don't blame them. Contractor drafting, while not new, is still a small phenomenon. There aren't a lot of us out there who do work with companies who already have full time CAD staff.
I replied to a job ad looking for a full time civil CAD drafter stating that I was available for contract civil CAD drafting and if they couldn't find someone to be an employee, give me a call. The firm called me in for an interview and gave me a 'test' project to try me out. They had a spare CAD station so off I went. The client was immediately satisfied and after asking about my availability, he put his hiring plans on hold. Over the next year, the client used me for a variety of civil projects using Land Desktop until they found a full time drafter. Then I was able to bring the new drafter up to speed on the client's CAD standards and brought him up to speed on Land Desktop's abilities.
Working with this company was great for both of us. It allowed the client to hold out hiring a full time drafter until the work load really justified it, keeping their cost down. They could just call me when they knew ahead of time when there was a large project coming due. If their projects were in for agency review and there was minimal work for a week or two, they didn't have to pay a full time employee to sit there and do nothing.
Contract drafting works.