Hi, you might get someone else's ideas to get you past the BS but
Even if you give them a pencil sketch on graph paper as to your ideas they can't complain that much. I have been in construction for quite a while and even the fancy drawings and the best of the best engineering groups can't stand up and talk to there own engineer over the cubicle wall (sorry rant over)
You are the designer,engineer,architect for your platform.
Grab some paper,pencil and eraser and give them an idea about what's in your head.
It will be easier to explain later when things weren't quite rite than later when you have to say the project idea I submitted wasn't mine and I never planned on following it I was just trying to pacify you?
I have a few discussions like that one way or the other with my daily work and I can say that it is better to be upfront with everything and speak your mind? It will make some mad at first but in the end you have there respect.
Sorry I started venting/ranting again
Scribble your idea on some paper and at the bottom right say idea for construction and the same if they want an elevation of holding tanks under the bus frame? Scribble an idea and bottom right say idea for construction? There not in charge of vehicle/rv construction but they do follow a RV construction code so look at that. It covers the piping,electrical,venting,propane stuff which is the only thing they should have authority over and please correct me if I am wrong.