There is the photo archive at http://www.vintageairstream.com/archives/index.html
-- that might give you some ideas for other models of similar length. I can't say I've seen a specific resource for alternate plans.
It might be a good idea to weigh things you remove from the trailer and make sure any new design doesn't add beyond that weight. This size trailer didn't have much margin between empty and GVWR -- especially with just one axle. Do you have any info in an owners manual about loading?
With children will you want a sit-down dinette? Dropping the dinette for a bed truly sleeps just one once they grow to any size. Put a bunk up over that?