Campaign bus of Larry Hogan, Republican nominee for Maryland governor. ( John Wagner/The Washington Post)

The Maryland Democratic Party filed a complaint late Tuesday alleging that the campaign of Republican gubernatorial nominee Larry Hogan is, in effect, not paying full fare for its campaign bus.

For the past three months, as he pursues an upset victory over Lt. Gov. Anthony G. Brown (D), Hogan has been traveling the state in a rock-star-sized recreational vehicle adorned with his campaign logo.

The vehicle was purchased personally by Hogan, an Anne Arundel County businessman, and his campaign is reimbursing the candidate $683.77 a month for its use, according to Hogan spokesman Adam Dubitsky. That’s the equivalent of Hogan’s monthly payment on the RV, which Dubitsky called perfectly reasonable.

In the complaint, however, the Democrats contend that the payment is far less than the “fair-market value” of the vehicle. And under elections law, the party says, that’s what the campaign should be paying for the bus.

To bolster its case, the Maryland Democratic Party submitted estimates that suggest that the cost of operating an RV the size of Hogan’s is between $500 and $700 a day — about what the Hogan campaign is paying per month. The campaign, the complaint says, is “grossly undervaluing” the cost of the RV — a claim Dubitsky vigorously disputed.

The issue takes on added importance because Hogan is participating in the state’s public financing system, which limits his campaign to spending about $2.6 million on the race.

In effect, every dollar that Hogan uses to pay for his bus is a dollar that can’t be spent on television ads or other voter outreach.

In an interview last week, before the complaint was filed, Jared DeMarinis, director of the candidacy and campaign finance division of the State Board of Elections, said that covering the monthly payments on a vehicle is generally considered to be a “reasonable” standard for such situations.

But DeMarinis said he wouldn’t comment on a particular complaint until after one was filed.