On my trailer they are behind the door trim molding. The size of the hole depends on how accurately you can place it as well as the size of the nut. I think I'd just locate the 4 holes as accurately as possible and then drill them so the edge would be just under the molding, i.e. as big as possible without showing.
Dealer fixed mine for $150 while I was in having a panel replaced.
Be careful - the nuts are not secured in any way. If you drop one, it will be in the wall forever. A nut plate would have cost what, $0.75?
“You cannot reason someone out of a position they have not been reasoned into"
Al, K5TAN and Missy, N4RGO WBCCI 1322
2002 Classic 30 Slideout -S/OS #004
2013 Dodge 2500 Laramie 4x4 Megacab Cummins