OK, The extender has arrived. The stock holes are at 41" and 48" pin to pin. Using the 41" holes the receiver is still 6" past the back edge of the camper. I feel correct length will be 36"
Looking for advice from those who have flat towed. I assume that the hitch should be more or less flush to the back of the tow vehicle (camper). Is there any reason to leave it longer? I am fine with cutting it down and drilling a new hole. The holes in the extension and in the hitch don't align properly anyway.
Thanks again