The battery conductors aren't rated for 70A, don't get a charger with a higher current rating. 

I can't imagine how the existing charger couldn't keep up with your electrical demand unless something is wrong. Dual batteries is not your problem. Either the batteries aren't holding a charge or the existing converter isn't working properly or you have an excessive load or short circuit somewhere. You will need to find out which.

First, check what 12V DC loads you have on. Is the refrigerator on 12Vdc? If so, change it to propane or 120Vac. Have you accidentally pulled your breakaway brake pin? That is the plastic pin on the tongue which is connected to the cable that you hook to the tow vehicle so that the trailer brakes are energized if the trailer gets unhitched. Besides those two relatively heavy loads there really aren't any 12V loads in the trailer that use very much power. Turn them all off anyway.  

How old are you batteries? If they are flooded batteries are the plates covered with electrolyte when you remove the caps? 

If those easy to check things aren't the problem then you will want to get a multimeter to explore further. Get one that has a clamp on that can measure DC currents (not just AC currents). That will make troubleshooting much easier. 

Yep...all the above plus, if you were to upgrade, the new converter might cause your 30 amp supply breaker to trip IF you were trying to power the microwave and/or A/C and/or electric water heater element while that large converter is pulling a lot of amperage also.

You really need to figure out what is wrong, rather than chase this with expensive upgrades that may or may not fix the problem, or might even make it worse.

+1 on staying with the 55A converter. If you are considering changing to an LiFePO4 battery, WFCO offers a drop-in replacement converter that is 50A suitable for LiFePO4 batteries but not for Pb-Acid batteries. However, that would make necessary other changes as you can see in my mods.

As for Progressive Dynamics, they are more expensive and while they are good, they too can fail as I have read in some of the reviews. I think WFCO got a bad batch of converters. I had one fail, but after replacing that, the replacement was still going strong until I replaced it with the LiFePO4 capable converter, which is working very well. When I was at the Kentucky  Mini-Mini a couple of years ago, I found from Dave Hickey who was working on them who did a write-up on Facebook in the RPod Owner's Group there) that one of the causes was that the grounding screws were not making good contact, eventually would cause a cold-soldered contact point to fail. Re-soldering this connection and making sure the screws attaching the circuit board to the mount are tight seemed to be a way to prevent this from happening. Here is a link to that article:

https://www.facebook.com/groups/RPodOwners/permalink/10155633270460808 - https://www.facebook.com/groups/RPodOwners/permalink/10155633270460808