They suggest to kill the breaker so the plug (at the van and the end of the extension cord) won't pick up a load which will cause damage to the plug due to arcing. Killing the power or dropping the load can be done in the van at the main or at the source provided there is some type of switch or breaker. You should avoid plugging a hot extension cord when possible. Eventually the plug can create heat and lead to electrical failure and possibly become a fire hazard. I bought a heavy amp construction GFI jumper (it's a couple feet long) and use it as a switch at the source. With the GFI indicator off, I plug into the van and then turn on the GFI. Arcing can also occur while pulling out the plug, so I also turn it off before un-plugging. I really do not need to go into the van unless I have to turn something on. My solar does most of the charging so no reason to climb in. The best way would be to build a dedicated 50 amp box that has a breaker in it and turn that breaker on and off so you're not putting needless wear on your internal breaker in the van. I would rather have problems with a box at home than a breaker in the van on the road. For the most part, breakers are not designed as switches rather as safety devices. The jumper might not handle heavy loads such as the Starcool (it would have to be rated about 50 amps) and can only supply the smaller loads to things like battery charging, the refrigerator, fans and stuff like that. So if there is no way to keep the power cord dead while plugging it in, your breaker in the van will be your only choice unless you install a rated electrical switch. A rated electrical switch made for continuous operation is definitely better than breaker or even a GFI especially if you have no idea how to change out breakers.
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