No, the battery fuse or CB will be in the 40-60 amp range to match the ampacity of the wire and the charging amps of the OEM converter at 45-55a say.
It would be quite close to the battery, on the tongue of a TT just under the battery box, eg.
EDIT--the CB bottom right with the two black wires is a possible, but not sure what the bigger thing on the left is with the red wires. The isolator above appears to be for alternator charging of the house batts, controlled by the ignition being on or off. I am not familiar with that set-up, but a friend has one in a Sunseeker Class C. Our 1991 C does not have that set-up.
Somebody else who has one of these arrangements could help with this question better than I.