Charging the battery with generator issue

You really should share your expertise with WFCO tech support so that you can correct them. The WFCO in one of my trailers will not pass convert 12v from my Honda 3000, UNLESS THE GROUND & NEUTRAL ARE BONDED. The same with a neighbor. Remove the bond plug = fail. Reinstall the bond and it works. Tech support advised contrary to your remark so contact them and advise that your advice supersedes.

I have nothing else in between the trailer plug and the generator, so please advise why it fails.

I'll agree with Mr. Wizard here. If there's no "surge protector" type of device in the RV blocking the AC to the converter, then I'd suspect something like a bad minus connection from the converter output, causing the AC bond to carry the converter's DC output, or alternatively an open neutral at the converter, causing the ground wire to carry the neutral side of the AC power. Easiest way to find the sure answer is to check for AC power at the converter's plug, or run an extension cord to connect the converter directly to the generator.