Usually, the standard size for most camper trailer frames is 48 by 96. I used this frame for my camper, and I love it because it provides extra space and feels sturdy.
The most recommended option is creating a design that will allow natural lighting during the day. You also need to consider the light source when the sun goes down.
Depending on your trailer design and budget, you can choose to include your camper with the basic amenities or even get a full-fledged plumbing system.