Seadeep, don't know what to tell you about curtains but you may want to look into replacing the seats rather then re-upholstering, I have talked to alot of people (where I work) who thought they would re-upholster until they found out what it cost. You can replace a back to back seat for $100 a jump seat for $70 or a pedestal type seat for $130, customers have told me numerous times they were quoted anywhere from $500 to $1000 for re-uphostery work.
Just something to think about if you haven't already.

As for trailer work, Glenns welding in Lynnwood does good work, might want to give them a call. (425)743-2226 or http://www.gweld.com