It sounds like the client is not really wanting a
sign that can be changed out every two years. That sounds like a deception to get what he wants—the cheapest possible lighted
sign by ignoring industry standards and best practices.
I am tempted to suggest raising the price significantly on the "pillowcase" version to make it unattractive. On second thought, doing a job this way is not something I would expect from a reputable
sign company.
I would pass on this job and let someone else have it.
I would then watch the job and see how it holds up.
It would also be nice to have night and day pictures of the finished job for your own use.
A client like this may be good to avoid. They may present nothing but problems in the future.
Brad