So after working for like 8 hours over the last two days, I finally have a tank wagon design that I really like the look of. I based it off of pics from here
https://www.bluebell-railway.co.uk/bluebell/wagon/1921.html , getting the ladder to fit properly was a pain in the ass and took up most of the designing time to get it just right.
Not a big fan of how it looks in all black though since it's just looks like a mass of black plastic at the moment, so I'll probably change the color of the tank for something else (Dark blue or yellow maybe?).