I've sort of looked at that.
I usually work using the following...
The number of people = double the number of feet in the foot space under the table = the number of dinner sized plates on the table.
In our small truck campers, with the number of people = 3, I find that the feet under the table don't have enough room, unless someone has their feet on top of another persons feet, and the dinner sized plates don't fit very well on the table.
So, take some measurements of feet and dinner sized plates, then make the table the size you want and then figure out the size the foot space under the table is going to be (usually the same size as the table if you want to convert the dinette into a bunk) and lastly, then figure out what size the seats are going to be.
Does it all fit?
If that works out OK and everything can all fit comfortably then go for it.
Might be easier to have the regular 2 person dinette (a table that can go farther towards the outside wall, i.e., a bigger table) with a portable seat/stool that feet can be tucked under (or along the sides) when sitting, located in the center of the camper (at the inside end of the table). That's what I do when we have 3 of us camping. Usually the cook sits down last, so (s)he gets the stool in the center of the camper.