Interior fuse keeps blowing

Turn all lights off and check the current flow. Should be zero.
Then turn on one light at a time and discover where the current goes to.

Otherwise you need to discover what is on that circuit and where the power is going.

Main power cord is 120vac and does not really have an effect on the 12vdc system.

One thing for sure is that it is not a short circuit. If it was the C/B would blow immediately. So it's got to be an overload.

As suggested, do some checking as maybe something else is running on the same circuit. Simple check, turn the fridge off, pull the suspect fuse, get a meter and measure the resistance on the outgoing side of the fuse. It should read "open". If not, then something else is connected to the circuit such that as the fridge controller "works", it heats up and eventually blows the limit of the fuse.... maybe. Of course, it will help if you identify the size of fuse involved and the fridge model to look at things like "draw".

Other things that may be running are the radio memory and the propane detector, carbon monoxide sensor. Or there could just be a wire someplace that has been compromised by a staple or other sharp edge.
This one is going to take some detective work by removing one thing and then another to see what happens. You really need an ohm meter to try to track down this shot.
I would not replace the fuse and leave the rig though.