I would not do campaigns, that can afford focus groups, this way.
I would ask my core party constituency to answer a number of questions. The questions would be how you justify your own parties’ position on such and such issues.
For example I would ask most Republicans how they justify the Republican Party denying the validity of legal abortions when nearly all Republicans support keeping abortions legal.
I would ask most Democrats how they justify the Democratic party's complete subservience to labor unions when nearly no Democrats would ever join a union.
It is the answers to these questions that will allow voters to cross party lines.
For example most Republicans know that abortion has been a dead legislative issue for many decades and abortions will be legal no matter who is elected.
Most Democrats would say unions are a declining institution of no particular importance. Therefore it is easy to ignore the union's role in the Democratic Party.
There are at least half a dozen issues on both sides that the adamant partisans are able to dismiss because they have explanations similar to the ones above.
In a campaign, these explanations need to be used openly to allow others to cross party lines.