Well how much time do you have and how big a hurry are you in.

If you are stopping off at North Rim of the Grand Canyon,  Jacobs lake area. It's very pretty and covered with large Ponderosa Pines. 7200 feet elevation and lots cooler than South Rim and the drive over Page.  Driving through Page will take you past Lake Powell. Unless you are going to rent a boat, You will just be looking at large lake in a desert when you go past Powell.

I prefer to come up Hiway 89 vs I-15.  A little slower,  but a whole lot more scenic.  89 is a two lane hiway that follows the Sevier River . There are several roads that you can use to cross over to I-15 from Hiway 89.

Hiway 14 at Long Valley.  Climbs up past Duck Creek, Navajo Lake and down into Cedar City.  The decent into Cedar is pretty steep and if you are not comfortable with your trailer my not be the best first time drive.  But I have hauled my horse trailer over it several times. And there  are lots of RV and 5th wheelers that use this road. 

Hiway 20 (Bear Valley Junction north of Panguitch) is a favorite with the truckers cutting between I-15 and 89.  It does gain a lot of elevation. Has some steep parts. Gives you a great view when you pass over the pass. And it's an easier drive than hiway 14.

Personally I'd stop at Ruby's Inn, Eat their Buffet dinner and enjoy a few hours in Bryce Canyon and Red Mountain. They are not far off Hiway 89.  It may even be a good half way point for your trip. Stay the night in your new trailer or rent a room. Then use Hiway 20 to cut over to I-15 for the rest of the trip home. Ruby's Inn has a Rodeo ground and horse motel. You can easily park your trailer there while you drive into the Park or do some area sightseeing. The grand Staircase National park is also very nearby.

The Milford Flat fire has Burned A LOT of the area along I-15 ( almost 600 square miles) So a lot of the drive between Beaver and Fillmore is just black. Staying on Hiway 89 will avoid most of the fire damage and let you enjoy the mountain scenery. You can take Hiway 50 from Richfield to Scipio or hiway 28 from Gunnison to Levan to cut back over to I-15 farther north of the Burn area.

If you are a Shakespear fan.  Catch a play in Cedar City are.