For sealing and protecting the outlet valve of the propane tanks, consider this guy:
https://www.amazon.com/gp/product/B07BB1Q5MT/ref=ppx_yo_dt_b_asin_title_o03__o00_s00?ie=UTF8&psc=1
It is O-ring sealed and works like a charm. Considering everyone in here is complaining about the DOT approved tank bracket, I assume most won't be interested, but I have been very pleased with it. Literally the only thread on cap I could find anywhere on the internet for propane tank threads.
On the topic (ish), I bought that protector cap after I was having flow issues out of my propane tank after it ate dust on my swing out for 8 days in Utah. I ran into a problem with my 5lb tank not being able to feed both burners of my camp chef stove at decent/full flow. It could run a single burner enough to boil water, but running both burners it would fall on its face. Thought maybe my 5lb was empty but I filled it at a fuel stop and the guy said it only took about 2lbs of propane and that it was plenty full. Later at home I tore down the stove, cleaned everything, and tested with a 1lb disposable bottle and both burners ran hotter than hell. switched back to my 5lb on the adapter hose and it was clearly not flowing as much. I bought a new adapter hose thinking it may be clogged with dust and dirt. Got home, cranked up the burners for a second on the 5lb and both were running full blast. Nice, hot, and loud. Thought I fixed my problem but with more use I've realized that my 5lb flows enough to run both burners full hot for the first second or so, then the burners noticeably reduce in flame size/heat. this leads me to believe it's some kind of supply issue with the tank... locking up in phase change from liquid to vapor, feeding vapor instead of liquid or vice versa, etc. I ruled out a blockage from the aforementioned dust because it flows enough for the first second or so.
It's a flame King tank- pre-purged from factory.
has anyone else had issues running a refillable tank to feed 2x 20k BTU burners at full tilt? Not sure if there's a pick up tube in the 5lb tank to pull liquid, or if its pulling vapors off the top which may be an issue. I assume the camp stoves are designed for liquid considering they feed from 1lb bottles that are inverted and I assume the 1lb bottles don't have pick up tubes, thus when inverted feeding liquid to the stove hardline.
Trying to exhaust my options before throwing money at a new tank with my fingers crossed... Any help is appreciated!