It is much safer to disconnect the negative first.
When you disconnect the negative you only need to worry about hitting the positive terminal with the wrench. Hitting anything else metal will do nothing.
When you then disconnect the positive, you only need to watch out for the negative terminal because the chassis is no longer "ground"
If you reverse and do the positive first, any slip that hits a metal part of the camper will cause a dead short and a shower of sparks. Worse yet it can weld the wrench to the frame and cause a fire.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW