Automated SpaCover

We are a Spa Pool manufacturer [login to view URL] The problem with spas is they have these big heavy covers to lift on and off. see [login to view URL] These are very hard to get on and off, especially for a large spa that is 4.5m x 2.3m We are wanting an automated cover that goes on and off just like a garage roller door. There is a company that does something similar to what we want.. See video [login to view URL] The Requirements will be for 3 sizes 4.5m x 2.3m 4m x 2.3m 2.3m x 2.3m Preferably since they are all 2.3m wide, we have only 1 unit and we can add or subtract the inside cover to suit whatever length we need. The one in the video is great but we dont want the end to be bulky like they have. We want the attachment to be as small as possible. (See my drawing on the attatchment)  More Requirements *The cover needs to be light weight * It needs to be able to insulate the heat * We also need to think of how stop the heat from the spa escape the edges of the spa. * It needs to be operated with a key (So kids cannot open) * It needs to be motorised. * I need to keep the costs down, so we need to think of what materials we are to use