I have never filed one or used a filled one but I have some questions/statements for people to think about.
1. What makes the store bought ones safer than the filled ones?
Store bought ones do leak just like refilled ones can. Last year I had a couple stored in a tote with lid, I opened the lid and smelt strong gas, I immediately put lid back and took tote outside to air out. My opinion, either new or refilled can leak making both dangerous.
2. Just thinking.
If Manufactors did make 1 lbers safe to refill. How long would they be in business? If they can make 5 lbers safe they can make 1 ibers safe to refill. That right there makes me wonder if the manufactors main reason for saying DO NOT REFILL is to keep sales up. If every 1 lber was safe to refill, allot more people would be doing it and sales would fall way down for new ones.
3. Common sense tells me the tanks sidewalls/valves/seals are made strong enough to refill.
If they wasn't then how could they be safe right out of the store? Since no refilling propain store will refill them, the manufactors have to stamp them "DO NOT REFILL" to stop customers from refilling.
4.
I believe the people who are trained and work at propain refilling stations could fill them safely if they wanted. But there's very little profit for them to mess with 1-Lbers so they don't. And Tom Dick and Harry aren't trained so it can be hazardous for them.
They do sell refilliable 1-lb tanks, heres a link. No idea the cost, doesn't say.
http://www.mantank.com/green/refillable.htm