I would not recommend hooking up a MiFi to any other router unless you can do so via USB. If your MiFi only have the wireless output option you will lose a substantial amount of the speeds that are available with your connection. If you are going to connect your MiFi via USB you will need to verify that the device you are buying will be compatible with the router you buy.
Now, personally, I would never use a router with a MiFi UNLESS that router can also do WiFi as WAN. This option allows you to create one router based wireless setup in your RV and then use either the campground WiFi (to save data charges) or your cellular connection without having to change your in-house network each time you select a different connection option.