Here are links for some useful forms and info.
Architectural Committee Project Application Form
Architectural Project Examples
Changes to your manufactured or mobile home
A building permit is usually required for structural changes to manufactured homes. In Washington state, an L&I alteration permit is required for structural changes, such as adding a room, garage, deck, windows, awning, or porch. In most cases, plan approval by L&I is required before construction.
Here is a link for a one page PDF with info