The Democrat-leaning Public Policy Polling firm has been actively polling marriage and other political topics state-by-state recently. They include an observation about a trend line they are seeing favoring the protection of marriage in their analysis of Missouri voters:

"59% of voters in Missouri think that gay marriage should be illegal, compared to just 32% who would like to see it become legal. But when you throw civil unions into the equation 62% of voters support some form of legal recognition for gay couples to only 37% opposed to giving same sex couples any sorts of rights. The 62% breaks down 28% for whom full gay marriage rights is their first choice and 34% who prefer civil unions. This is what we're seeing in most states- voters are uncomfortable giving the label 'marriage' to gay relationships...but they're ok with granting those couples more rights as long as it's called something else."