It should be right behind your breaker/fuse panel, located as tderonne indicated. If it's a Schumacher converter may look like a sheet metal box (with vent fans) attached to the back of your electrical panel box. Just replaced my Schumaker converter/charge with a Progressive Dynamics units - tired of the battery maintenance issues and noise.
Greg and Karen, the pups Bailey and Lily (St. Bernard mix and Beagle mix) and Lola (the attack cat)
On the 35U its under the bottom drawer below the stove. You have to pull the drawer completely out to access it.
It should be a 40 AMP MagnaTec and really is not that great for your batteries. I also replaced mine with a Progressive Dynamics with the Charge Wizard.
In that location you really should be pulling the draw out a few times a season to check for objects falling from the drawers above it potentially plugging the cooling vents and to vacuum up accumulated dust.
2001 Winnebago Adventurer WFG35U