Mother-in-Law rapid on the A section is rated class III, but it is more of a class II at lower flows. Red Creek Rapid on the B section can be worth scouting at higher flows, but there are lots of choices for a smaller boat. Flows are very predictable, they publish a release schedule. I have floated it countless times in my 9' mini cat.
The ramp below the dam is very tight and crowded. No parking allowed, just drop off. The busiest time is early morning when the pro guides are launching drift boats. There is a staging area in a parking lot above, you are supposed to rig up ready to launch then drive down to the ramp. They want you on and off the ramp in 15 minutes or less, seriously.
If you can launch after 10:00 you have a lot more room and time. Flaming Gorge Lodge and Trout Creek Ltd. are local outfitters that can set up a shuttle. They can also meet you at the upper lot with a flat bed and shuttle you down to the ramp for a drop off.
Another option is to float the A section with just day gear then stop at Little Hole to load up. Little Hole has tons of room and three ramp areas. The first float in camp is just a 1/4 mile or so down from Little Hole.
If you have time stop at the James Jarvey Historical Site along the C section.