Don't know your summers, don't know your heat... but the first thing that comes to mind is venting.

Cruising Sailors Forum Archive

I can't imagine it is a good idea to "greenhouse" a boat for any length of time.

But again, that is really just a quick opinion... maybe others have done it just fine.

winter cover in summer
- Don't know your summers, don't know your heat... but the first thing that comes to mind is venting.
  - I tried it and didn't like it but I've seen it done many