I know what you mean. You'll need to talk to them about the benefits of it.
On the same subject, I just finished making laminated cards this evening for my Service plans. I made business cards on the computer, and have boxes that I can use a hole punch on. I already have a laminator collectiong dust, so I put it to work......Look good.....
Sorry, but no pics....
I offer 3 types of plans....
~3 month bi-weekly (washes and a mini detail)
~3 month weeky (10 washes and 2 mini details)
~wash and vacs from 1 month to 6 months
I make sure I tell the customer about the plans, and let them know that a detail should be performed aound every 4 months. I also tell them, if they purchase a "plan", (me being the only one cleaning up the car) that the next full detail will be discounted, pending vehicle condition of course.