Here is what I did for a cheap effective gun oven.
What you see in the picture is a double wall vent pipe I bought at Home Depot for about $18. It's wrapped in pipe insulation which may or may not be necessary.
It sits on a hotplate which has a tempreture control. When you buy one of these make sure it's one with the "old style" eye and not a solid plate. Those don't seem to work as good.
The top is a simple paint can lid with an eye hook to hold the barreled action and a BBQ thermometer (Home Depot $5.)
It's simple, requires no tools except for putting a hole in a paint can lid and it works like a charm.
Hope this helps,
Terry