Re: Difference Between.....
Yeah basically if it's more about starting with a cargo van/passenger van it goes in Ground up. If it belongs to an established RV (even if that was originally a ground up build), in "Projects, DIY".
Imagine the person who just bought an E350 with a Quigley and one seat and wants to turn it into something- the Ground Up section is for him, because otherwise he would have to dig through tons of posts about swapping outlets, or changing over to LED lights when it is more likely they will be looking for how to put paneling and then lights up in the first place.
When in doubt, post. If it's terribly out of sync one of the admins will move it as appropriate.