Depending what you choose to put in the space, you can find one to fit with little or no modification. As stated, measure, and then shop. DH just installed ours, it was relatively easy, and is an almost perfect fit. We did not get a large refer.
Caution...most manufacturers won't honor the warranty if installed in an RV. I've read that Samsung will, so if that's important to you, check it out. I know for a fact Frigidaire won't. Ours only cost $491.00, so we weren't really worried about the warranty since I couldn't find a Samsung to fit.
Also, make sure you plug in the new refer BEFORE installing it in your RV to make sure it works. Who would've thought ours would be defective from the factory? We didn't think to make sure it worked, so now we're having to take it out of the RV and put another one in.
Also, read up on these forums about the inverter. Some of the models need a pure sine inverter, which ours is not. Since we never boondock, we've decided to only run ours on shore power. From what I've read, it'll stay cool while traveling if you're careful about how often you open the door. When you stop for lunch, you can run the genny which will power it for a little while and then plug it in when you stop at your destination.