Hi Eddie,
You have two different cover brands in your pictures. Not that, that is an issue, I'm just seeing the differences. If you look, one has square covers, the other round corners. Those covers become brittle over time from sun exposure, and then crack, and you have a mess inside if it rains. A prior owner has replaced them, most likely a few times. After 10 years of living outside all the time, they do go bad from sun damage.
What Sunline installed originally was a Ventline brand nominal 14 x 14" roof vent, as they call it in the RV industry. Ventline has been sold, and Dexter now owns the brand, but it is still being made under the Ventline brand. And the all-new, post-2008 frame, I think, Ventline's new roof vent covers are different from the old style. They now call them Ventadome. The roof hood design is different.
But you can still buy the old covers to fit your camper and most other Sunlines newer than yours. Heads up, there are lots of brands selling these replacement covers. And the hinge is different over the years, even within the Ventline brand.
This is a Ventline cover with the correct hinge at Etrailer.
https://www.etrailer.com/RV-Vents-and-Fans/Ventline/BV0554-01.html If you do not buy one from them, make sure the hinge looks correct.
They show many pictures of what you are getting. I have bought from them many times and have had good experiences.
Since you are new to this, I'll expand a little on changing them.
1. Inside the camper, you need to remove the plastic trim (garnish) from the ceiling. Heads up, dirt and insects hide in that garnish. Take care not to dump the mess all over when it comes down.
2. Remove the crank knob. A center screw holds it in, and it has splines to connect to the crank-up gearbox.
3. Take down the screen. There are 2 screws that can be installed to hold up the screen. Sometimes the screws are not installed, but if they are, the screw goes into the metal frame. Take them out if they are there. Then there are little metal bent teeth near the screw area, you have to flex carefully the screen plastic inward on the sides to unhook the teeth. Do one side at a time. Be careful, the screen gets brittle from the sun, too, and will crack.
4. Take the 2 screws out of the crank gear box, and that will allow you to unhook the lid lift arm from the vent cover up on the roof. You may have to use the crank handle to lift the lid up a little to get the lift arm out of the lid.
Once you have the lift arm off the lid, go up on the roof to remove the cover. Bring a pair of needle-nose pliers. Pivot the lid up and use the pliers to bend the metal tab at the end of the hinge so it matches the hinge's metal circle. Then lift up the cover and slide the hinge off the metal roof frame.
To install, reverse the process and bend each end tab inward to prevent the cover from shifting out of position.
HEADS UP: The roof on your Sunline is not a direct, "walk-on roof". There is no decking under the roof membrane to support your weight. To service an item on the roof, you need to do this:
Start from the side of the roof on a ladder, for steps 1 to 3
1. Use a tarp, cloth, moving blanket, etc., to lay on the roof where you will work to protect the roof membrane from abrasion.
2. Get 3/8" or thicker, small plywood sheets that can span the rafters to support your weight. I use 2 ft x 4 ft 3/8 sheets of plywood, and sometimes 30" by 40", as that is what I have. The smaller pieces are manageable to carry up the ladder and place on the roof over the tarp/blanket, etc. You use as many small sheets as needed for the job you are doing.
3. The rafters are on nominal 16" centers, but not always. Some are closer together. Make sure the plywood sheets span over the rafters. You can feel the roof for the stiff rafter, as the membrane will sag some, but remain stiff over the rafter.
4. Be very careful getting on and off the roof. Have a good, solid, stable ladder. Here are a few pics of the process to help show this.
A tip: if you treat the new vent covers with 303 UV protectant, inside and out, before you install them, it will help them last longer.
303® Aerospace Protectant. It is sold at many places, such as Walmart, some Auto Parts stores, and Amazon etc. That same 303 can be used on any plastic or vinyl on the camper, including roof parts, siding decals, cargo doors, etc. It also helps the rubber, too.
I hope this helps,
John
PS. I will be back tomorrow to answer your questions about roof cleaning and sealant treatment to help keep water out. Good for you for asking