The voltage drop from wire resistance in an overly small extension cord has to go somewhere and that somewhere is heat.
(Think possible fire; sparks and a BIG expense in ruined RV electronics (just about everything in your camper could be damaged from low voltage as well as high - think "Brownout")
A long run has higher resistance than a short one.
A thicker wire has less resistance than a narrow one.
Don't send a boy...
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