My stock boat cover deteriorated to the point that I needed a new one. It had poles to hold up the middle so water would just roll off. The replacement I bought looks like the image below. It does not have poles and pools with water after every rain. What can I do to fix this? Is there something I can buy or a DIY solution for pitching a tent?
You basically answered your own question. You need some kind of frame that will create a sufficiently sloped roof. Having the frame on the outside will always create a small depression in the middle where water will accumulate.
As a workaround, it may help to pull the cover tighter and also offer some slope forward towards the drawbar.
How to create such a frame is really depending on the exact shape of your boat and possible attachment points.