The best retrofit I've seen is in the Murphy's rig.  
I have two portable burners.  One is in the motorhome and the other at our house.  I use them outdoors for hot, sizzle cooking of steaks, chops and fillets.  I've abandon BBQs for a 10" Lodge cast iron pan.   
I've never found a dominant brand.  Each time I look, I see new brands.  And, all seem to get pretty good reviews.