First, since you mention that you might be going RV'ing full time--where are you going to setup a frame? Light & portable does not exactly go with long throated machine. Also, quilting machines--especially mid & long arm machines are single function--no fancy stitches and most don't have feed dogs. Stitch regulators are another story. The stitch regulators on most machines are actually a sensor mechanism that mounts on the carriage of the quilting frame and senses how fast/slow you are going and cuts into the speed of the machine to try and control your stitch length. Bernina is the only sit-down machine I know of with a stitch regulator. Supposedly other folks had come up with a 3rd party stitch length regulator that went on the actual machine and not the carriage but I never saw such a gizmo in the wild except for Bernina. I think Viking had something called a Fabric Mover that may have worked similarly.
So--if you find a way to setup & store a quilting frame in an RV--you're going to want one that is easily taken apart and put back together again--that knocks out a bunch of them.
From what you've described--I think you'll want to check out the Janome Horizon and Viking Sapphire. Those will give you a longer throat, fancy stitches and are sort of portable if you're strong and don't have to carry it very far. The stitch regulation is going to be a problem unless Quilters Cruise Control now makes a module for one of those machines. They did not for my Elna 7200 when I first bought it so I just learned to regulate myself. If you find that the frame is going to be a problem, stitch regulation isn't going to work for you anyway unless you go with the Bernina which is well over your budget.