Hello Jeff Davis,
If the garage is attached & was not part of the manufactured unit that came from the  manufacturer then it would be considered a modification & a structural inspection would be needed to ensure the following guidelines are met: 

• Modifications to the Manufactured Home

Additions or structural modifications may bring the original unit out of compliance with the HUD Manufactured Home Construction

Safety Standards (MHCSS) and make the home ineligible.

However, manufactured homes that have an addition or have had a structural modification may be eligible:

If the state in which the property is located requires inspection by a state agency to approve modifications to the property and

there is confirmation that the property has met the requirements.

If the state does not have these requirements, the property must be inspected by a licensed professional engineer who can

certify that the addition or structural changes were completed in accordance with the HUD Manufactured Home Construction

Safety Standards.

Original question: