A while back I did design and 3D print a mounting bracket and leg extenders to add on a thermal camera, with gimbal. Technically it did work, but the camera and gimbal I wanted to use were just a bit too heavy. It did fly, but the flight time was dramatically reduced and I didn't feel it was as stable as I wanted. However, if you had a lesser, lighter thermal camera, and maybe didn't use a gimbal, or a lighter gimbal (since the camera would be lighter), it may fly better.
I also had a video transmitter and receiver for the other controller I used to control the camera and gimbal. So again, if you went a little more spartan, you wouldn't need as much extra gear on there.
This was on a P4A.
Andy