The new Dometic I installed a couple years ago came with a much thicker shroud, when compared to either the OEM units or the replacement unit I installed 7-8 years ago. In addition to the general dimensions of the shroud, you have to ensure the foam air dams glued to the underside, are correctly positions to isolate air flow going thru the external condensor coil. Without the proper foam dividers, the unit will be much less efficient. Think I would go back to Dometic and get the shroud designed for your unit.
2003 40' MDTS
Garden Ridge, Texas