Back in my broke college days in San Marcos, we'd load a 16' canoe on my Wrangler with no rack. I'd drop the top (never was up anyway) and we'd lay the boat, on gunwale pads, across the roll bar and windshield. Once it was tied down, it wasn't going anywhere. Solid as a rock.
Of course a rack is far less ghetto, but you do what you gotta do sometimes.