You should always list the type of RV you have (85 26ft Itasca) in a post even if it is in your profile. I assume you have the Sunflyer model. Makes life much easier for those your asking to help you as many do not know how to see your profile.
Winnebago used the 6300 Series MagneTek (now Parallax) Power Center with a Linear Converter in 85 (PPS LINEAR CONVERTERS
). These converters had a battery charger installed and also a built in transfer relay that selected battery or converter power as the 12VDC source.
The inverter was most likely an add on by a previous owner so you will have to trace the wiring to see how they hooked it up.
Trickle charger is only designed to maintain a charge, not recharge a depleted battery.
Fridge should work off of converter however with batteries disconnected this style of converter would not have a filtered output (noisy) so it can damage sensitive equipment with no battery connected (http://www.parallaxpower.com/6300/LinearFAQ.pdf