I'm assuming you will be taking I-15 from LV to Idaho Falls, but if you wanted to take a little detour over toward Twin Falls, I recommend seeing Shoshone Falls. The falls are very impressive.
Also, City of Rocks National Preserve near Almo, ID is very interesting. It was a stop-off along the Oregon Trail and has granite rocks and spires surrounding a prairie-like area where the wagon trains used to camp. You can see where pioneers wrote their names on the rocks.
On your way up I-15 near Idaho Falls, the town of Blackfoot has the Idaho Potato Museum
. It only costs a few dollars to get in, and they have room in their lot to park RVs so you can stop on your through town.
will take you to the part of our blog where we covered southern Idaho.
Enjoy your trip.