MY trailer window about 4X7 and would like to expand it to 10X12 or something like that.
Camping trailer or mobile home?
doublewide mobile home
Have you thought about adding a bay window?
If you want a 10 x 12 window you might consider a french door rather than a window. You will have to have a contractor tell you what you can do structurally. How tall are your mobile home walls? A 10 x 12 window may not fit.
Here is one more link for you
French door or sliding glass door.