I’m in the process of updating my 62 Globetrotter and am looking to upgrade my systems. One of the areas I’m looking to upgrade is the Gray (nonexistent), Black(Above sub-floor in rear), Holding(leaking 30 gallon tank in the front of the cabin.) tank. I need some help...
Can/How do I replace my old holding tanks under my sub-floor? where do I put them. I'm going to the welder in the next week or so, what do I need to know to successfully implement these systems. Attached are pictures of my frame please feel free too photoshop and repost to help visualize if needed.
I guess, I’m also calling out Andy. What do I need to buy from you to get these systems up and running, I’d love to give you my money...

thanks everyone for the help