Quart or two of Dap Weldwood from Walmart (cheapest I've found). Use a $10 (sale price) spray gun from Harbor Freight. Cheaper than 3M and the working time is longer which is good if you are a first timer. Throw gun out when you are done.

Dap also sells a vinyl top glue made for spraying, but I don't think it's any different than the contact cement they sell in the quart or gallon cans.

As mentioned above, I use the gel because it's easy to brush and less mess... may take longer to apply, but has worked great for me.