Re: Starcraft Chieftain 1972 MK4
You can fabricate your own custom hatch rings out of aluminum angle, you can buy this angle at Home Depot or Lowes.
The foam you have packed around your fuel tanks is a big mistake:
That foam is not a fuel resistant foam and it only takes a few drops of gasoline to melt a whole bunch of that foam, if your tank(s) ever leak you'll have a huge mess of white goo and no support for your tanks.
The correct foam to use around fuel tanks is the 2 part expanding urethane foam.