If you do upgrade, you will get much faster battery charging with an intelligent multi-stage charger, even if you go with the same amp...
My converter is under the kitchen counter, plugged into a wall socket. The cables run to the fuse pannel by the stairs, and just connect to the buss that the positive battery cable is connected to.
It should be pretty simple to put a new converter in your setup. There's just the 110ac connection and the negative and positive 12v connection.
If I were in your shoes, though, I think I'd unhook the old coverter at the power box, mount the new one someplace handy, and run bigger wire directly from the converter to your battery box. It might be handy to add a catastrophic failure type fuse (say 100 amp)while you are messing with it.
For my use, a bigger converter would be very handy, as I mostly camp in primitive areas, and sometimes in cold weather. The furnace uses a lot of juice, and it would be nice to minimize the generator run time needed to recharge.
If you generally camp with hookups, though, then there wouldn't be much point in spending the money to get a converter bigger than the 45 amp you are looking at, IMHO.
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