You can use strip... if you size the strip to match the loss resistance of the tube alternative, there are still a couple of disadvantages.
One likely disadvantage is that you'll probably get lower voltage handling at high power, but that can be mitigated by rounding and smoothing corners and edges near the capacitor.
Another disadvantage is supporting the strip so it doesn't move at all... if it moves, the tuning will probably change.
But you can make an effective magloop out of flat strip.
Something to remember about the losses is that it's not as simple as matching *surface area* with the tube equivalent. Because of the current distribution on the strip you need more surface area of strip to match the performance of a round tube. I suspect that weight for weight, you can often get equal or better performance with a strip b/c you can't get tube with a thin enough wall.
There is always a catch. One other ham has had pretty good success with a spiral wrapped Loop on PVC pipe.http://www.eham.net/articles/26572
Here is the article that was featured on eHam.
The Nay sayers will come out of the woodwork to shoot this guy down, but I would build it, if I wasn't strapped for cash right now. Present administration has me worried about my IRS Tax bill due on Apr 15.