Here's a
LINK to the Trailer Life Towing Guides. They are a wealth of information.
A quick look at the 2011 Guide shows your Navigator has a tow rating of 8700 pounds. If you figure the dry weight of your trailer and add around 500-1000 pounds of your 'stuff' then you might get a realistic idea of how much weight you'll be dragging around. It appears that the trailers you're looking at will be able to be towed by what you currently own. You might not have to get a new tow vehicle.
BTW, the 2014's have about the same tow rating as your 2011.