ISO propane tank for 1990 Dodge Chinook

[Lady AT Tramp]

Looking for a propane tank for a 1990 Dodge Chinook conversion van/Class B motorhome. We believe it to be about a 12 gallon tank. Would also need assistance (either referral or from seller) to correctly install as this will be the first time we do anything with a fixed propane tank of any kind.

 

[Gary RV_Wizard]

You need an ASME (American Society of Mechanical Engineers) spec fixed propane tank to comply with US standards. I believe ASME is the ISO standards authority for pressure vessels in the USA, so their specs should be ISO compliant as well.  Get a tank of whatever size and shape fits in the available space - there are many variations. Here's one that might work:

https://www.amazon.com/Flame-King-YSN122-Horizontal-Propane/dp/B01M1BUQ3U

Tanks may be either welded or bolted in place. Connections to the RV propane plumbing are basic plumbing stuff, usually requiring just a couple of wrenches.
Here is a video of a DIY install in an RV bus conversion.
https://www.youtube.com/watch?v=3xnQvcvbquU
And this how-to for a van installation:
https://www.vanlifeoutfitters.com/installing-a-propane-tank-underneath-a-promaster-van-with-remote-fill-kit/