Ok your truck alternator is doing its job perfectly, and newish batteries eliminates that problem. The only thing Im wondering is arent most campers designed to charge the camper battery during driving thru the harness? esp if you have a 5 or 7 pin connector?
Also let me get your setup straight: you are running an INverter to a CONverter to charge the camper battery? ie. Truck alternator to INverter to CONverter to "house" battery. Is that right? (probably not)
I am going thru a 1986 Prowler Lynx wiring setup due to a prev owner screwing the wires all up. What I discovered is there are 3 positive wires connected to the "house" battery. One from the Converter for charging during shore power, One from the house batt going to the 12v fuse box in camper, and one going from the house batt to the trailer harness for charging during towing.
Although I've never checked the conn at the truck plug, after reading your post I'm curious now as to exactly how much voltage/amperage I'm getting there.
As far as your options you listed, C sounds the best senario you have going. The 35 amp is working right? maybe not as fast as you'd like though.
Have you thot about running two 6 volt batteries in series? you will get much longer use per charge that way.