Yes there are. No aquarium but enough to find for hot fluids but there is no need to.....
By te way, an aquarium pump will work if you just pump air into the bath from out of a corner. The fluid will float arround.

Most simple thing is using a simple plate of aluminium or a bit niicer an old flat Pentium or 486 heatsink, mount the heaters and sensor on it and hang it in the bath. If you do that, besure the sleeve will stay put, one headbolt with a spacer is enough.