I found this from the MV-426B directions:
"Vehicle Type - If the vehicle type is a mobile home, "mobile home" should be specified in the "Other" block.Mobile homes do not need to be inspected by an enhanced vehicle safety inspector and an inspection sticker does not need to be affixed to Form MV-426B. A detailed description of how the mobile home was reconstructed must be attached to your application along with interior and exterior photographs. Your application must be signed by a certified document reviewer and forwarded to PennDOT for processing.
Can it be that they actually eliminated a step from the old form? I would attach receipt copies of everything I put in along with pics. I would verify that mobile home means motorhome. I have no idea what a "certified doc reviewer" is but they sound better to deal with than an "inspector."
I found these directions which specify modifying from bus to motorhome:
http://www.dot10.state.pa.us/pdotforms/ ... -recon.pdf