Bitty Squaredrop questions

Hi, guys!!!! I am so excited! I've been watching videos for a few months now. Other than my youngest, the rest of my family is pretty much uninterested and ignoring my latest obsession. Even I wasn't entirely sure if I was going to drop the ball on this one.
Yesterday, I made a decision. A small trailer isn't a good long term solution, but a large one is going to cost me more than I ought to spend on something that may end up being dropped due to finances or lack of knowledge.. Worst case scenario, if I drop the ball and don't make another, I still have a trailer, which can be used for hauling trash or whatever.
So, anyway, yesterday afternoonI bought a used 4.5ish' by 6' trailer from a guy upgrading to a larger one. There's a little bit of surface rust on it, so I stopped at Lowe's and picked up a wire brush and some of the rust prevention paint spray to put on over it. I was wondering how to tell if I've scrubbed long enough? The areas without rust don't seem to do anything when I scrub them, so I'm guessing I should just scrub until nothing more flakes off... but maybe I am wrong there?
I originally was going to bribe my teenagers to brush it for me due to sensory issues, but I decided that I wouldn't until I made sure that I really COULDN'T do it myself. I got home and tried. Lo and behold, it was nothing like I'd anticipated and I will be doing it MYSELF, thank you very much. This is my project and I'm not going to fail straight out of the gate because I didn't bother to even try.
Sooooo, here's my question. I love the youtube videos, but I need more. Are there any books on building squaredrop campers that I can actually read in detail? Plans, either for free, or not too expensive? I'm trying to keep this as cheap as possible, since I can't really afford a. LOT.
Also, the trailer says it can hold up to 2,000 lbs. However, what I don't know how to do is to figure out how much weight the floor can support safely.
Second, I don't know how to calculate how much weight the walls can support for shelves, cabinets, folding down furniture and whatnot.
Lastly, I need to figure out how tall or square I can build it before it starts to mess with my mpg. I'm currently driving a Prius Prime, which is a smallish car, but I'm hoping to upgrade to a RAV4 before the thing is done being built.
That's another thing -- if I don't get the RAV4, there's no point in building a big one, since the Prius probably can't pull it. How do I find this information? Thank you!!!!
Yesterday, I made a decision. A small trailer isn't a good long term solution, but a large one is going to cost me more than I ought to spend on something that may end up being dropped due to finances or lack of knowledge.. Worst case scenario, if I drop the ball and don't make another, I still have a trailer, which can be used for hauling trash or whatever.
So, anyway, yesterday afternoonI bought a used 4.5ish' by 6' trailer from a guy upgrading to a larger one. There's a little bit of surface rust on it, so I stopped at Lowe's and picked up a wire brush and some of the rust prevention paint spray to put on over it. I was wondering how to tell if I've scrubbed long enough? The areas without rust don't seem to do anything when I scrub them, so I'm guessing I should just scrub until nothing more flakes off... but maybe I am wrong there?
I originally was going to bribe my teenagers to brush it for me due to sensory issues, but I decided that I wouldn't until I made sure that I really COULDN'T do it myself. I got home and tried. Lo and behold, it was nothing like I'd anticipated and I will be doing it MYSELF, thank you very much. This is my project and I'm not going to fail straight out of the gate because I didn't bother to even try.
Sooooo, here's my question. I love the youtube videos, but I need more. Are there any books on building squaredrop campers that I can actually read in detail? Plans, either for free, or not too expensive? I'm trying to keep this as cheap as possible, since I can't really afford a. LOT.
Also, the trailer says it can hold up to 2,000 lbs. However, what I don't know how to do is to figure out how much weight the floor can support safely.
Second, I don't know how to calculate how much weight the walls can support for shelves, cabinets, folding down furniture and whatnot.
Lastly, I need to figure out how tall or square I can build it before it starts to mess with my mpg. I'm currently driving a Prius Prime, which is a smallish car, but I'm hoping to upgrade to a RAV4 before the thing is done being built.
That's another thing -- if I don't get the RAV4, there's no point in building a big one, since the Prius probably can't pull it. How do I find this information? Thank you!!!!