Welcome!! You may not need a larger tank -- you will be amazed at how little propane the fridge takes. The furnace is the real propane hog, but you may not need that much (except during shower time).
What kind of batteries do you have, and how old are they? For extended boondocking or dry camping, I use two group 31 batteries. My 120 watt solar panel usually keeps them fully charged, but I camp in very sunny places -- not sure if the west coast of Canada gets as much sun. Where on the west coast do you live?
Make sure never to let your batteries get down below 12.1 volts -- otherwise, their useful lives will be much shorter than if they are kept fully charged as much as possible.
Also, since this is your first trailer, be sure to ask lots of questions. We were all newbies once upon a time.