Scott McDaniels from the Van's prototype shop covers some details and helpful tips about building an RV fuel tank in this walkthrough video. You can use this information in combination with your plans to better understand how the pros approach the process.

0:00 Introduction
1:26 Overview, prep and assembly tips
7:26 Tank sealing philosophy
11:02 Flange install, basic techniques
33:53 Installing Stiffeners
43:05 Prep rib
56:45 Install rib
1:23:53 Outboard end rib
1:42:44 Inboard end rib
1:47:35 Fittings
1:50:28 Rear baffle intro
1:54:49 Baffle wall sealant
2:09:48 Install baffle wall
2:22:13 Zbracket install
2:35:29 Conclusion/WrapUp