I was a conductor on the Cog Train for 3 summers and my future wife, whom I met as a waitress on the top of Pikes Peak, worked there 8 summers. We both have had a lot of experience with both the road, train, and trail.
1) Your Thor Vegas should have no problem with the trip to the summit. On the way down you will want to use the engine to help maintain a lower speed (i.e. use a lower gear) and avoid riding the brakes. They will stop you at Glen Cove to check your brakes and make you stop if they are hot. Stopping at Glen Cove on the way down is a good idea anyway since there are things to see there as well. Using a lower gear and being easy on the brakes will make the trip a snap. The road is somewhat windy, so you won't be flying along anyway. (Check your RV they do have some size restrictions for the road.)
2) The road is paved all the way to the summit. Back in the day it was gravel the last 6 miles. It's a nice, well maintained road. Check on activities that might be going on when you plan to go. There is the Pikes Peak Hill Climb each year (professional car racers), and I've seen a cycling race going up the mountain when I was last there visiting. It is a beautiful trip on the road, but make sure you check the weather report. It can snow in the summer at the higher altitudes.
3) The Cog train is a fantastic way to go from Manitou Springs to the summit. Beautiful scenery and tour. The downside is you are limited to the amount of time you can spend on the summit. Back in my conductor days it was a 40 minute summit stop (it may have changed since my conductor days... so, check first). For most people that was plenty of time.
4) The hike is definitely a long day trip. It's a nice hike, but you need to be in shape to hike the Bar Trail. Many people make it a two day camping trip, which is much more pleasant.
5) Altitude - It is over 14,000 feet so you most likely feel the lack of oxygen, especially on your way down the hill. That is when people tend to get drowsy. If you have any heart issues, it's not a place for you. And, they will not allow infants go up to that altitude. Many of the passengers on the train slept on the trip back down (3hr 10min round trip). Working there it took me about a week to acclimate to the altitude on the summit.
6) On the summit - Take it easy and move slowly. You may feel faint or breathless if you run around, or move too quickly. Take your time and sit and put your head between your knees if you feel light-headed. Some people hyperventilate occasionally and you can use a paper bag to breathe with if that happens. Don't let this scare you off. Most people do just fine.
7) Be careful on what and how much you eat on the summit. I would avoid carbonated drinks. I can't tell you how many times people got sick on the way back down on the train after eating chili dogs and drinking coke.

One last item. If you have kids with you, there is an amusement park at the base of the mountain on the road up Pikes Peak. It is called the North Pole and is a fun place for the kids.
I hope this little synopsis helped. It's a trip you don't want to miss if you have the opportunity. Best wishes.
Doug