Well we can’t spoon feed the new folks all the information contained in the other threads , but we can present them with a SIMPLE shape , and let them go from there ...
About the sizes , I think it should follow the user’s trailer size ... Since foam can easily be added to or subtracted from the 4’X8’ sheet (unlike plywood ) Material size is of a lesser consideration , so everything doesn’t have to be the old 4’X8’ standard ... keeping with close to “square” proportions in cross section would be good , favoring wider , rather than taller .. wheels outside of the cabin width .. maximum “roll” stability that way ... as example , a 60” wide trailer frame , would also have a cabin height ~ 60 “ ... Simple !!!
for a Standard , all those Teardrops are “adorably Cute” , but more difficult to construct ... So I’d think a simple rectangular Box with a simple but aerodynamic nose would be easy for anybody ... and a great introduction into Foamies '... You and I know , these things are like Potato chips (crisps) ... You can’t have just the one ...

The “second’ one can be something more Curvy , once some basic foamworking (hey , a new word ) skills are learned ...
So here’s yet another drawing , to get things going ... about as simple as it gets , all sized on the X (your number here . preferably the width of the trailer frame ) measure, everything square or quarter square ... save the nose, that is aerodynamic , yet easy to build ...
