NEW YORK (MarketWatch) -- Mobile Mini Inc.'s said Friday that its fourth-quarter earnings fell to $12.4 million, or 36 cents a share, from $14 million, or 38 cents a share, a year earlier, hurt in part by higher expenses. In addition, the Tempe, Ariz., maker of portable storage systems said it agreed to merge with privately held Mobile Storage Group in a deal valued around $701.5 million. Mobile Mini said it will assume about $535 million of Mobile Storage Group's outstanding debt and acquire all of the company's outstanding shares for $12.5 million in cash and shares of newly issued Mobile Mini convertible preferred stock with a liquidation preference of $154 million. That stock will be convertible into about 8.55 million Mobile Mini common shares, representing a conversion price of $18 per Mobile Mini share and resulting in ownership in Mobile Mini of about 19.8% for Mobile Storage stockholders. Mobile Mini said the deal is expected to "slightly" add to earnings in 2008. The deal could close as early as June. On Thursday, Mobile Mini shares closed down 59 cents, or 3.7%, at $15.26.